Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 31, 2015	Apr. 28, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Entity Registrant Name	U.S. Silica Holdings, Inc.
Entity Central Index Key	0001524741
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		53,391,504

Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current Assets:
Cash and cash equivalents	$ 252,555	$ 267,281
Short-term investments	75,253	75,143
Accounts receivable, net	96,355	120,881
Inventories, net	65,035	66,712
Prepaid expenses and other current assets	10,775	9,267
Deferred income taxes, net	23,776	22,295
Income tax deposits	0	746
Total current assets	523,749	562,325
Property, plant and mine development, net	565,337	565,755
Goodwill	68,647	68,647
Trade names	14,914	14,914
Customer relationships, net	6,824	6,984
Other assets	13,882	12,317
Total assets	1,193,353	1,230,942
Current Liabilities:
Book overdraft	6,756	4,215
Accounts payable	56,699	85,781
Dividends payable	6,738	6,805
Accrued liabilities	13,922	17,911
Accrued interest	60	60
Current portion of long-term debt	3,321	3,329
Deferred revenue	26,771	26,771
Income tax payable	4,997	0
Total current liabilities	119,264	144,872
Long-term debt	490,873	491,757
Deferred revenue	59,224	64,722
Liability for pension and other post-retirement benefits	61,554	59,932
Deferred income taxes, net	47,918	49,749
Other long-term obligations	16,472	16,094
Total liabilities	795,305	827,126
Stockholders’ Equity:
Preferred stock	0	0
Common stock	540	539
Additional paid-in capital	193,140	191,086
Retained earnings	240,683	232,551
Treasury stock, at cost	(16,156)	(542)
Accumulated other comprehensive loss	(20,159)	(19,818)
Total stockholders’ equity	398,048	403,816
Total liabilities and stockholders’ equity	$ 1,193,353	$ 1,230,942

Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Sales	$ 203,958	$ 180,095
Cost of goods sold (excluding depreciation, depletion and amortization)	138,653	126,770
Operating expenses
Selling, general and administrative	26,961	15,445
Depreciation, depletion and amortization	13,243	9,589
Total operating expenses	40,204	25,034
Operating income	25,101	28,291
Other (expense) income
Interest expense	(6,836)	(3,808)
Other income, net, including interest income	11	38
Total other (expenses) income	(6,825)	(3,770)
Income before income taxes	18,276	24,521
Income tax expense	(3,453)	(6,150)
Net income	$ 14,823	$ 18,371
Earnings per share:
Basic (in usd per share)	$ 0.28	$ 0.34
Diluted (in usd per share)	$ 0.27	$ 0.34

Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 14,823	$ 18,371
Other comprehensive income:
Unrealized gain (loss) on derivatives (net of tax of $2 and $(12) for the three months ended March 31, 2015 and 2014, respectively)	3	(19)
Unrealized gain (loss) on investments (net of tax of $22 and $19 for the three months ended March 31, 2015 and 2014, respectively)	35	29
Pension and other post-retirement benefits liability adjustment (net of tax of $(235) and $95 for the three months ended March 31, 2015 and 2014, respectively)	(379)	149
Comprehensive income	$ 14,482	$ 18,530

Condensed Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Unrealized gain (loss) on derivatives (net of tax of $2 and $(12) for the three months ended March 31, 2015 and 2014, respectively)	$ 2	$ (12)
Unrealized gain (loss) on investments (net of tax of $22 and $19 for the three months ended March 31, 2015 and 2014, respectively)	22	19
Pension and other post-retirement benefits liability adjustment (net of tax of $(235) and $95 for the three months ended March 31, 2015 and 2014, respectively)	$ (235)	$ 95

Condensed Consolidated Statements of Stockholders' Equity (USD $)	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings (Deficit)	Accumulated Other Comprehensive Income (Loss)
Balance at December 31, 2014 at Dec. 31, 2014	$ 403,816,000	$ 539,000	$ (542,000)	$ 191,086,000	$ 232,551,000	$ (19,818,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	14,823,000				14,823,000
Unrealized loss on derivatives	3,000					3,000
Unrealized loss on short-term investments	35,000					35,000
Pension and postretirement liability	(379,000)					(379,000)
Cash dividend declared ($0.125 per share)	(6,691,000)				(6,691,000)
Common stock-based compensation plans activity:	2,090,000			2,090,000
Equity-based compensation	6,000			6,000
Unrealized loss on short-term investments	43,000		85,000	(42,000)
Pension and postretirement liability	(443,000)	1,000	(444,000)
Repurchase of common stock	(15,255,000)		(15,255,000)
Balance at March 31, 2015 at Mar. 31, 2015	$ 398,048,000	$ 540,000	$ (16,156,000)	$ 193,140,000	$ 240,683,000	$ (20,159,000)

Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating activities:
Net income	$ 14,823	$ 18,371
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	13,243	9,589
Debt issuance amortization	352	220
Original issue discount amortization	96	66
Deferred income taxes	(3,101)	1,160
Deferred revenue	(5,498)	0
(Gain)/loss on disposal of property, plant and equipment	(32)	0
Equity-based compensation	2,090	1,330
Excess tax benefit from equity-based compensation	(6)	(1,438)
Other	2,630	117
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	21,344	(22,985)
Inventories	1,677	13,041
Prepaid expenses and other current assets	(1,512)	(1,173)
Income taxes	5,742	3,049
Accounts payable and accrued liabilities	(33,071)	9,111
Liability for pension and other post-retirement benefits	1,007	(151)
Net cash provided by operating activities	19,784	30,307
Investing activities:
Capital expenditures	(13,377)	(10,606)
Proceeds from sale of property, plant and equipment	72	0
Net cash used in investing activities	(13,305)	(10,606)
Financing activities:
Dividends paid	(6,758)	(13,402)
Repurchase of common stock	(15,255)	0
Proceeds from options exercised	43	3,004
Excess tax benefit from equity-based compensation	6	1,438
Tax payments related to shares withheld for vested restricted stock	(443)	(229)
Repayment of long-term debt	(1,275)	(938)
Change in book overdraft	2,541	(2,130)
Financing fees	(64)	0
Net cash used in financing activities	(21,205)	(12,257)
Net increase/(decrease) in cash and cash equivalents	(14,726)	7,444
Cash and cash equivalents, beginning of period	267,281	78,256
Cash and cash equivalents, end of period	252,555	85,700
Cash paid during the period for:
Interest	5,529	3,824
Taxes	$ 805	$ 2,043

Summary of Significant Accounting Policies	3 Months Ended
Summary of Significant Accounting Policies	Mar. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	NOTE A—SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation and Consolidation The accompanying Condensed Consolidated Financial Statements (the “Financial Statements”) of U.S. Silica Holdings, Inc. (“Holdings,” and together with its subsidiaries “we,” “us” or the “Company”) included in this Quarterly Report on Form 10-Q , have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X issued by the U.S. Securities and Exchange Commission (“SEC”). They do not contain certain information included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2014; therefore, the interim Condensed Consolidated Financial Statements should be read in conjunction with that Annual Report on Form 10-K. In the opinion of management, all adjustments necessary for a fair presentation of the Financial Statements have been included. Such adjustments are of a normal, recurring nature. We have reclassified certain immaterial amounts in the prior years’ assets section of the consolidated balance sheets and operating activities section of the consolidated statement of cash flows to conform to the current year presentation. These reclassifications had no effect on previously reported total assets and net cash flows from operations. In order to make this report easier to read, we refer throughout to (i) our Condensed Consolidated Balance Sheets as our “Balance Sheets,” (ii) our Condensed Consolidated Statements of Operations as our “Income Statements,” and (iii) our Condensed Consolidated Statements of Cash Flows as our “Cash Flows.” Unaudited Interim Financial Statements The accompanying Balance Sheet as of March 31, 2015; the Income Statements for the three months ended March 31, 2015 and 2014; the Condensed Consolidated Statements of Comprehensive Income for the three months ended March 31, 2015 and 2014; the Condensed Consolidated Statements of Stockholders' Equity for the three months ended March 31, 2015; the Cash Flows for the three months ended March 31, 2015 and 2014; and other information disclosed in the related notes are unaudited. The Balance Sheet as of December 31, 2014 was derived from our audited consolidated financial statements as included in our 2014 Annual Report. Use of Estimates and Assumptions The preparation of the Financial Statements requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and the related disclosure of contingent assets and liabilities at the date of the Financial Statements and the reported amounts of revenues and expenses during the reporting period. The more significant areas requiring the use of management estimates and assumptions relate to mineral reserves that are the basis for future cash flow estimates utilized in impairment calculations and units-of-production amortization calculations; environmental, reclamation and closure obligations; estimates of recoverable minerals; estimates of allowance for doubtful accounts; estimates of fair value for certain reporting units and asset impairments (including impairments of goodwill and other long-lived assets); write-downs of inventory to net realizable value; equity-based compensation expense; post-employment, post-retirement and other employee benefit liabilities; valuation allowances for deferred tax assets; reserves for contingencies and litigation; and the fair value and accounting treatment of financial instruments including derivative instruments. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances. Accordingly, actual results may differ significantly from these estimates under different assumptions or conditions. Recently Issued Accounting Pronouncements In April 2015, the Financial Accounting Standards Board ("FASB") issued an Accounting Standards Update, Interest-Imputation of Interest, which simplifies presentation of debt issuance costs. The new standard requires that debt issuance costs be presented in the balance sheet as a direct deduction from the carrying amount of debt liability, consistent with debt discounts or premiums. The new standard will be effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within fiscal years beginning after December 15, 2016. Early adoption of the amendments in this Update is permitted for financial statements that have not been previously issued. We have elected to adopt the standard early and have presented debt issuance costs as a direct deduction from the carrying amount of debt on our Balance Sheets as of March 31, 2015 and December 31, 2014.

Earnings Per Share

3 Months Ended

Mar. 31, 2015

Earnings Per Share [Abstract]

Earnings Per Share

NOTE B—EARNINGS PER SHARE

Basic earnings per common share is computed by dividing income available to common stockholders by the weighted average number of common shares outstanding for the period. Diluted earnings per common share is computed similarly to basic income per common share except that the weighted average number of common shares outstanding is increased to include the number of additional common shares that would have been outstanding if the potentially dilutive common shares had been issued. In accordance with the applicable accounting guidance for calculating earnings per share, we did not include in our calculation of diluted earnings per share for the applicable periods stock options where the exercise prices were greater than the average market prices.



	Three Months Ended March 31,
	2015			2014
Net income	$	14,823		$	18,371
Less: net income allocated to outstanding restricted stockholders	(46		)	(42		)
Net income allocated to common stockholders	$	14,777		$	18,329
Weighted-average common stock
Outstanding	53,416			53,505
Outstanding assuming dilution	53,869			54,054

The weighted-average stock options (in thousands) that are antidilutive and are therefore excluded from the calculation of diluted earnings per common share are:



	Three Months Ended March 31,
	2015	2014
Weighted-average outstanding stock options excluded	306	—

Capital Structure and Accumulated Comprehensive Income

3 Months Ended

Mar. 31, 2015

Equity [Abstract]

Capital Structure and Accumulated Comprehensive Income

NOTE C—CAPITAL STRUCTURE AND ACCUMULATED COMPREHENSIVE INCOME

Common Stock

Our Amended and Restated Certificate of Incorporation, authorizes up to 500,000,000 shares of common stock, par value of $0.01. Subject to the rights of holders of any series of preferred stock, all of the voting power of the stockholders of Holdings shall be vested in the holders of the common stock. There were 53,374,963 shares of common stock issued and outstanding at March 31, 2015. As of March 31, 2014, there were 53,733,092 shares issued and outstanding.

In 2015, our Board of Directors declared quarterly cash dividends as follows:



Dividends per Common Share		Declaration Date	Record Date	Payable Date
$	0.125	February 12, 2015	March 16, 2015	April 3, 2015

All dividends were paid as scheduled.

Any determination to pay dividends and other distributions in cash, stock, or property by Holdings in the future will be at the discretion of our Board of Directors and will be dependent on then-existing conditions, including our business conditions, our financial condition, results of operations, liquidity, capital requirements, contractual restrictions including restrictive covenants contained in our debt agreements, and other factors. Additionally, because we are a holding company, our ability to pay dividends on our common stock may be limited by restrictions on the ability of our subsidiaries to pay dividends or make distributions to us, including restrictions under the terms of the agreements governing our indebtedness.

Preferred Stock

Our Amended and Restated Certificate of Incorporation authorizes our Board of Directors to issue up to 10,000,000 shares, in the aggregate, of preferred stock, par value of $0.01 in one or more series, to fix the powers, preferences and other rights of such series, and any qualifications, limitations or restrictions thereof, including the dividend rate, conversion rights, voting rights, redemption rights and liquidation preference, and to fix the number of shares to be included in any such series, without any further vote or action by our stockholders.

There are no shares of preferred stock issued or outstanding at March 31, 2015 and 2014. At present, we have no plans to issue any preferred stock.

Share Repurchase Program

We are authorized by our Board of Directors to repurchase shares of our outstanding common stock from time to time on the open market or in privately negotiated transactions. As of March 31, 2015, we are authorized to repurchase up to $50 million of our common stock through December 11, 2015. Stock repurchases, if any, will be funded using our available liquidity. The timing and amount of stock repurchases will depend on a variety of factors, including the market conditions as well as corporate and regulatory considerations. Under our share repurchase program, as of March 31, 2015, we have repurchased 706,093 shares of our common stock at an average price of $23.83 and are authorized to repurchase up to an additional $33.2 million of our common stock.

Accumulated Other Comprehensive Income

Accumulated other comprehensive income (loss) consists of fair value adjustments associated with cash flow hedges and accumulated adjustments for net experience losses and prior service cost related to employee benefit plans. The following table presents the changes in accumulated other comprehensive income by component during the three months ended March 31, 2015:



	For the Three Months Ended March 31, 2015
	Unrealized gain/(loss) on cash flow hedges			Unrealized gain/(loss) on short-term investments			Pension and other post-retirement benefits liability			Total
Beginning Balance	$	(134	)	$	(41	)	$	(19,643	)	$	(19,818	)
Other comprehensive income (loss) before reclassifications	(3		)	35			(856		)	(824		)
Amounts reclassed from accumulated other comprehensive income	6			—			477			483
Ending Balance	$	(131	)	$	(6	)	$	(20,022	)	$	(20,159	)

Amounts reclassed from accumulated other comprehensive income (loss) related to cash flow hedges category are included in interest expense in our Income Statements and amounts reclassed related to pension and other post-retirement benefits liability category are included in the computation of net periodic pension costs, respectively, at their before tax amounts.

Business Combination

3 Months Ended

Mar. 31, 2015

Business Combinations [Abstract]

Business Combinations

NOTE D—BUSINESS COMBINATIONS

On July 31, 2014, we completed our acquisition of Cadre Services, Inc. ("Cadre"), a regional sand mining company based in Voca, Texas, for approximately $98.3 million in cash.

The acquisition of Cadre resulted in goodwill of approximately $0.2 million, none of which is deductible for tax purposes. This amount represents the residual amount of the total purchase price after allocation to the assets acquired and liabilities assumed.

The table below represents the tangible and identifiable intangible assets and liabilities based on management’s assessment of the acquisition date fair value of the assets acquired and liabilities assumed:



Accounts receivable	$	6,898
Inventory	2,534
Other current assets	174
Fixed assets	73,138
Deferred tax assets (net)	13,966
Accounts payable, accrued expenses and other liabilities	(4,389		)
Net tangible assets acquired	92,321
Customer relationships	1,274
Trade Name	4,478
Goodwill	244
Purchase price, net of cash acquired	$	98,317

The value of acquired intangible assets and the related estimated useful lives consist of the following:



	Estimated Useful Lives	Value
Customer relationships	15 years	$	1,274
Trade name	Indefinite	4,478
Total intangible assets		$	5,752

Pro Forma Adjusted Summary

The results of Cadre’s operations have been included in the consolidated financial statements subsequent to the acquisition date.

The following unaudited pro forma consolidated financial information reflects the results of operations as if the Cadre acquisition had occurred on January 1, 2014, after giving effect to certain purchase accounting adjustments. This information does not purport to be indicative of the actual results that would have occurred if the acquisition had actually been completed on the date indicated, nor is it necessarily indicative of the future operating results or the financial position of the combined company:



	Three Months Ended March 31, 2015
Sales	$	188,509
Net income	$	18,417
Basic earnings per share	$	0.34
Diluted earnings per share	$	0.34

Property, Plant and Mine Development

3 Months Ended

Mar. 31, 2015

Property, Plant and Equipment [Abstract]

Property, Plant and Mine Development

NOTE G—PROPERTY, PLANT AND MINE DEVELOPMENT

At March 31, 2015 and December 31, 2014, property, plant and mine development consisted of the following:



	March 31, 2015			December 31, 2014
Mining property and mine development	$	197,824		$	197,824
Asset retirement cost	9,559			9,559
Land	28,443			28,443
Land improvements	35,420			35,322
Buildings	47,198			47,149
Machinery and equipment	331,604			323,618
Furniture and fixtures	1,599			1,599
Construction-in-progress	83,269			78,997
	734,916			722,511
Accumulated depletion, depreciation and amortization	(169,579		)	(156,756		)
Total property, plant and mine development, net	$	565,337		$	565,755

The amount of interest costs capitalized in property, plant and equipment was $42 and $201 for the three months ended March 31, 2015 and 2014, respectively.

Debt

3 Months Ended

Mar. 31, 2015

Debt Disclosure [Abstract]

Debt

NOTE H—DEBT

At March 31, 2015 and December 31, 2014, debt consisted of the following:



	March 31, 2015			December 31, 2014
Senior secured credit facility:
Revolver expiring July 23, 2018 (4.75% at March 31, 2015 and December 31, 2014)	$	—		$	—
Term loan facility—final maturity July 23, 2020 (4% - 5.25% at March 31, 2015 and December 31, 2014)	503,100			504,375
Less: Unamortized original issue discount	(1,983		)	(2,078		)
Less: Unamortized debt issuance cost	(6,923		)	(7,211		)
Total debt	494,194			495,086
Less: current portion	(3,321		)	(3,329		)
Total long-term portion of debt	$	490,873		$	491,757

Revolving Line-of-Credit

We have a $50 million revolving line-of-credit (the “Revolver”), with zero drawn and $3.1 million allocated for letters of credit as of March 31, 2015, leaving $46.9 million available under the Revolver.

Debt Maturities

At March 31, 2015, contractual maturities of long-term debt are as follows:



2015	$	3,825
2016	5,100
2017	5,100
2018	5,100
2019	5,100
Thereafter	478,875
	$	503,100

Our senior secured credit facility is secured by substantially all of our assets and a pledge of the equity interests in certain of our subsidiaries. The facility contains covenants that, among other things, govern our ability to create, incur or assume indebtedness and liens, to make acquisitions or investments, to pay dividends and to sell assets. The facility also requires us to maintain a consolidated total net leverage ratio of no more than 3.75:1.00 as of the last day of any fiscal quarter whenever usage of the Revolver (other than certain undrawn letters of credit) exceeds 25% of the Revolver commitment. As of March 31, 2015, we are in compliance with all covenants in accordance with our senior secured credit facility.

Asset Retirement Obligations

3 Months Ended

Mar. 31, 2015

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

NOTE I—ASSET RETIREMENT OBLIGATIONS

Mine reclamation costs, or future remediation costs for inactive mines, are accrued based on management’s best estimate at the end of each period of the costs expected to be incurred at a site. Such cost estimates include, where applicable, ongoing care, maintenance and monitoring costs. Changes in estimates at inactive mines are reflected in earnings in the period an estimate is revised.

As of March 31, 2015 and December 31, 2014, we had recorded a liability of $11.5 million and $11.3 million in other long-term obligations related to our asset retirement obligation. Changes in the asset retirement obligation during the three months ended March 31, 2015 and the year ended December 31, 2014, respectively, are as follows:



	March 31, 2015		December 31, 2014
Beginning balance	$	11,283	$	9,378
Payments	—		(782		)
Accretion	187		676
Additions and revisions of prior estimates	—		2,011
Ending balance	$	11,470	$	11,283

Fair Value Accounting

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Fair Value Accounting

NOTE J—FAIR VALUE ACCOUNTING

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Fair value is estimated by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement:

Level 1—Quoted prices in active markets for identical assets or liabilities.

Level 2—Observable inputs other than quoted prices in active markets for identical assets and liabilities, quote prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3—Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability.

Cash equivalents

Due to the short-term maturity, we believe our cash equivalent instruments at March 31, 2015 and December 31, 2014 approximate their reported carrying values.

Short-Term Investments

In general, the fair value of our short-term investments is based on quoted prices for similar assets in active markets, or for identical assets or similar assets in markets in which there were fewer transactions (Level 2). Money market mutual funds are based on calculated net asset value and are reported in Level 1. Variable rate demand obligations underwritten and remarketed by a financial institution are priced at par value.

Long-Term Debt, including current maturities

We believe that the fair values of our long-term debt, including current maturities, approximates their carrying values based on their effective interest rates compared to current market rates.

Derivative Instruments

The estimated fair value of our derivative assets (interest rate caps) are recorded at each reporting period and are based upon widely accepted valuation techniques, including discounted cash flow analysis on the expected cash flows of each derivative contract. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves and implied volatilities. We also incorporate credit valuation adjustments to appropriately reflect both our nonperformance risk as well as that of the respective counterparty in the fair value measurements.

Although we have determined that the majority of the inputs used to value our derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with our derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default of ourselves and our counterparties. However, as of March 31, 2015, we have assessed that the impact of the credit valuation adjustments on the overall valuation of our derivative positions is not significant. As a result, we have determined that our derivative valuations in their entirety are classified in Level 2 of the fair value hierarchy.

In accordance with the fair value hierarchy, the following table presents the fair value as of March 31, 2015 of those assets that we measure at fair value on a recurring basis:



	Level 1		Level 2		Total
Short-term investments	$	995	$	74,258	$	75,253
Interest rate derivatives	—		—		—
Net asset	$	995	$	74,258	$	75,253

Short-Term Investments

3 Months Ended

Mar. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Short-Term Investments

NOTE K—SHORT-TERM INVESTMENTS

We have segregated funds into designated accounts with investment brokers who manage our short-term investment portfolio. Those funds are held on an available-for-sale basis and are therefore reported at fair value on the balance sheet. The following table summarizes our available-for-sale short-term investments as of March 31, 2015:



	Aggregate Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Money market mutual funds	$	995	$	—	$	—		$	995
Cash	1		—		—			1
Fixed income securities:
Certificates of deposit	28,767		2		(7		)	28,762
Commercial paper	10,186		12		(1		)	10,197
Corporate notes and bonds	12,539		—		(7		)	12,532
Government agencies	16,673		6		(8		)	16,671
U.S. Treasuries	2,152		—		(3		)	2,149
Variable Rate Demand Obligations	3,946		—		—			3,946
Total available-for-sale investments	$	75,259	$	20	$	(26	)	$	75,253

As of March 31, 2015, we considered the declines in market value of our short-term investment portfolio to be temporary in nature and did not consider any of our investments other-than-temporarily impaired. We typically invest in highly-rated securities, and our investment policy generally limits the amount of credit exposure to any one issuer. The policy requires investments generally to be investment grade, with the primary objective of minimizing the potential risk of principal loss. Fair values were determined for each individual security in the investment portfolio. When evaluating an investment for other-than-temporary impairment, we review factors such as the length of time and extent to which fair value has been below its cost basis, the financial condition of the issuer and any changes thereto, changes in market interest rates, and our intent to sell, or whether it is more likely than not it will be required to sell, the investment before recovery of the investment’s cost basis. As of March 31, 2015, we did not recognize any impairment charges.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2015

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

NOTE L—COMMITMENTS AND CONTINGENCIES

Future Minimum Annual Commitments at March 31, 2015:



	Operating Leases		Minimum Purchase Commitments
2015	$	31,851	$	29,917
2016	45,069		30,464
2017	42,675		19,871
2018	41,026		15,754
2019	34,485		10,000
Thereafter	103,523		16,356
Total future lease and purchase commitments	$	298,629	$	122,362

Operating Leases

We are obligated under certain operating leases for railroad cars, office space, mining property, mining/processing equipment and transportation and other equipment. Certain operating lease agreements include options to purchase the equipment for fair market value at the end of the original lease term. In general, the above leases include renewal options and provide that we pay for all utilities, insurance, taxes and maintenance. Expense related to operating leases and rental agreements totaled approximately $10.0 million and $7.1 million for the three months ended March 31, 2015 and 2014, respectively. As of March 31, 2015, we have no obligations under a capital lease.

Minimum Purchase Commitments

We enter into service agreements with our transload service providers and transportation service providers. Some of these agreements require us to purchase a minimum amount of services over a specific period of time. Any inability to meet these minimum contract requirements requires us to pay a shortfall fee, which is based on the difference between the minimum amount contracted for and the actual amount purchased.

Other Commitments and Contingencies

Our operating subsidiary, U.S. Silica Company (“U.S. Silica”), has been named as a defendant in various product liability claims alleging silica exposure causing silicosis. During the three months ended March 31, 2015, no new claims were brought against U.S. Silica. As of March 31, 2015, there were 75 active silica-related products liability claims pending in which U.S. Silica is a defendant. Although the outcomes of these claims cannot be predicted with certainty, in the opinion of management, it is not reasonably possible that the ultimate resolution of these matters will have a material adverse effect on our financial position or results of operations that exceeds the accrual amounts.

For periods prior to 1986, U.S. Silica had numerous insurance policies and an indemnity from a former owner that covered silicosis claims. In the fourth quarter of 2012, U.S. Silica settled all rights under the indemnity and its underlying insurance. The settlement was received during the first quarter of 2013. As a result of the settlement, the indemnity and related policies are no longer available to U.S. Silica and U.S. Silica will not seek reimbursement for any defense costs or claim payments. Other insurance policies, however, continue to remain available to U.S. Silica.

We have recorded estimated liabilities for these claims in other long-term obligations as well as estimated recoveries under the indemnity agreement and an estimate of future recoveries under insurance in other assets on our consolidated balance sheets. As of both March 31, 2015, and December 31, 2014 other non-current assets included $311 for insurance for third-party products liability claims and other long-term obligations included $1.6 million in third-party products claims liability.

Additionally, we recently received an unfavorable ruling in an arbitration proceeding as a result of exiting a toll manufacturing contract. The amount of the ruling was approximately $7.6 million, which was fully accrued as selling, general and administrative expense in our Income Statement for the three months ended March 31, 2015. We have filed an appeal with the arbitration panel in this matter and intend to vigorously pursue all other legal actions available to us.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	NOTE M—INCOME TAXES For interim period reporting, we record income taxes using an estimated annual effective tax rate based upon projected annual income, forecasted permanent tax differences, discrete items and statutory rates in states in which we operate. At the end of each interim period, we update the estimated annual effective tax rate, and if the estimated tax rate changes based on new information, we make a cumulative adjustment in the period. We record the tax effect of an unusual or infrequently occurring item in the interim period in which it occurs as a discrete item of tax. In the three months ended March 31, 2015, we recorded a discrete tax benefit of $2.9 million, which relates to the accrual of approximately $7.6 million as described in Note L - Commitments and Contingencies. The effective tax rates were 19% and 25% for the three months ended March 31, 2015 and March 31, 2014, respectively. The tax rate for the three months ending March 31, 2015 would have been 25% without the discrete tax benefit. Historically, our actual effective tax rates have been lower than the statutory effective rate primarily due to the benefit received from statutory percentage depletion allowances. The deduction for statutory percentage depletion does not necessarily change proportionately to changes in income before income taxes.

Pension and Post-Retirement Benefits

3 Months Ended

Mar. 31, 2015

Compensation and Retirement Disclosure [Abstract]

Pension and Post-Retirement Benefits

NOTE N—PENSION AND POST-RETIREMENT BENEFITS

We maintain a single-employer noncontributory defined benefit pension plan covering certain employees. Net pension benefit cost recognized for the three months ended March 31, 2015 and 2014 are as follows:



	Three Months Ended March 31,
	2015			2014
Service cost	$	324		$	269
Interest cost	1,203			1,143
Expected return on plan assets	(1,375		)	(1,255		)
Net amortization and deferral	666			238
Net pension benefit costs	$	818		$	395

In addition, we provide defined benefit post-retirement health care and life insurance benefits to some employees. Net periodic post-retirement benefit cost recognized for the three months ended March 31, 2015 and 2014 are as follows:



	Three Months Ended March 31,
	2015			2014
Service cost	$	44		$	45
Interest cost	277			257
Expected return on plan assets	(1		)	(1		)
Net amortization and deferral	96			—
Net post-retirement costs	$	416		$	301

For the three months ended March 31, 2015, we made no contributions to the qualified pension plan and made $0.8 million in contributions during the three months ended March 31, 2014. Total expected employer funding contributions during the fiscal year ending December 31, 2015 are $1.7 million for the pension plan and $1.7 million for the post-retirement medical and life plan.

Obligations under Guarantees	3 Months Ended
Obligations under Guarantees	Mar. 31, 2015
Guarantees [Abstract]
Obligations Under Guarantees	NOTE O—OBLIGATIONS UNDER GUARANTEES We have indemnified Travelers Casualty and Surety Company of America (“Travelers”) against any loss Travelers may incur in the event that holders of surety bonds, issued on behalf of us by Travelers, execute the bonds. As of March 31, 2015, Travelers had $8.5 million in bonds outstanding for us. The majority of these bonds, $8.2 million, relate to reclamation requirements issued by various governmental authorities. Reclamation bonds remain outstanding until the mining area is reclaimed and the authority issues a formal release. The remaining bonds relate to such indefinite purposes as licenses, permits, and tax collection. U.S. Silica is the contingent guarantor of Kanawha Rail Corporation’s (“KRC”) obligations as lessee of 199 covered hopper railroad cars, which are used by U.S. Silica to ship sand to its customers. KRC’s obligation as lessee includes paying monthly rent of $66 thousand until June 30, 2015, maintaining the cars, paying for any cars damaged or destroyed, and indemnifying all other parties to the lease transaction against liabilities including any loss of certain tax benefits. By separate agreement between U.S. Silica and KRC, KRC may, upon the occurrence of certain events, assign the lease obligations to U.S. Silica, but none of these events have occurred.

Segment Reporting

3 Months Ended

Mar. 31, 2015

Segment Reporting [Abstract]

Segment Reporting

NOTE P—SEGMENT REPORTING

Our business is organized into two reportable segments, Oil & Gas Proppants and Industrial & Specialty Products, based on end markets. The reportable segments are consistent with how management views the markets that we serve and the financial information reviewed by the chief operating decision maker. We manage our Oil & Gas Proppants and Industrial & Specialty Products businesses as components of an enterprise for which separate information is available and is evaluated regularly by the chief operating decision maker in deciding how to allocate resources and assess performance.

An operating segment’s performance is primarily evaluated based on segment contribution margin, which excludes certain corporate costs not associated with the operations of the segment. These corporate costs are separately stated below and include costs that are related to functional areas such as operations management, corporate purchasing, accounting, treasury, information technology, legal and human resources. We believe that segment contribution margin, as defined above, is an appropriate measure for evaluating the operating performance of our segments. However, this measure should be considered in addition to, not a substitute for, or superior to, income from operations or other measures of financial performance prepared in accordance with generally accepted accounting principles. The other accounting policies of each of the two reporting segments are the same as those in Note A - Summary of Significant Accounting Policies of our Financial Statements.

In the Oil & Gas Proppants segment, we serve the oil and gas recovery market by providing fracturing sand, or “frac sand,” which is pumped down oil and natural gas wells to prop open rock fissures and increase the flow rate of oil and natural gas from the wells.

The Industrial & Specialty Products segment consists of over 250 products and materials used in a variety of industries including, container glass, fiberglass, specialty glass, flat glass, building products, fillers and extenders, foundry products, chemicals, recreation products and filtration products.

The following table presents sales and segment contribution margin for the reporting segments and other operating results not allocated to the reported segments for the three months ended March 31, 2015 and 2014:



	Three Months Ended March 31,
	2015			2014
Sales:
Oil & Gas Proppants	$	148,753		$	130,584
Industrial & Specialty Products	55,205			49,511
Total Sales	203,958			180,095
Segment contribution margin:
Oil & Gas Proppants	52,195			41,628
Industrial & Specialty Products	15,456			13,187
Total segment contribution margin	67,651			54,815
Operating activities excluded from segment cost of goods sold	(2,346		)	(1,490		)
Selling, general and administrative	(26,961		)	(15,445		)
Depreciation, depletion and amortization	(13,243		)	(9,589		)
Interest expense	(6,836		)	(3,808		)
Other income, net, including interest income	11			38
Income before income taxes	$	18,276		$	24,521

Asset information, including capital expenditures and depreciation, depletion, and amortization, by segment is not included in reports used by management in its monitoring of performance and, therefore, is not reported by segment. Goodwill of $68.6 million has been allocated to these segments with $47.9 million assigned to Oil & Gas Proppants and $20.7 million to Industrial & Specialty Products.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying Condensed Consolidated Financial Statements (the “Financial Statements”) of U.S. Silica Holdings, Inc. (“Holdings,” and together with its subsidiaries “we,” “us” or the “Company”) included in this Quarterly Report on Form 10-Q , have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X issued by the U.S. Securities and Exchange Commission (“SEC”). They do not contain certain information included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2014; therefore, the interim Condensed Consolidated Financial Statements should be read in conjunction with that Annual Report on Form 10-K. In the opinion of management, all adjustments necessary for a fair presentation of the Financial Statements have been included. Such adjustments are of a normal, recurring nature. We have reclassified certain immaterial amounts in the prior years’ assets section of the consolidated balance sheets and operating activities section of the consolidated statement of cash flows to conform to the current year presentation. These reclassifications had no effect on previously reported total assets and net cash flows from operations. In order to make this report easier to read, we refer throughout to (i) our Condensed Consolidated Balance Sheets as our “Balance Sheets,” (ii) our Condensed Consolidated Statements of Operations as our “Income Statements,” and (iii) our Condensed Consolidated Statements of Cash Flows as our “Cash Flows.”
Unaudited Interim Financial Statements	Unaudited Interim Financial Statements The accompanying Balance Sheet as of March 31, 2015; the Income Statements for the three months ended March 31, 2015 and 2014; the Condensed Consolidated Statements of Comprehensive Income for the three months ended March 31, 2015 and 2014; the Condensed Consolidated Statements of Stockholders' Equity for the three months ended March 31, 2015; the Cash Flows for the three months ended March 31, 2015 and 2014; and other information disclosed in the related notes are unaudited. The Balance Sheet as of December 31, 2014 was derived from our audited consolidated financial statements as included in our 2014 Annual Report.
Use of Estimates and Assumptions	Use of Estimates and Assumptions The preparation of the Financial Statements requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and the related disclosure of contingent assets and liabilities at the date of the Financial Statements and the reported amounts of revenues and expenses during the reporting period. The more significant areas requiring the use of management estimates and assumptions relate to mineral reserves that are the basis for future cash flow estimates utilized in impairment calculations and units-of-production amortization calculations; environmental, reclamation and closure obligations; estimates of recoverable minerals; estimates of allowance for doubtful accounts; estimates of fair value for certain reporting units and asset impairments (including impairments of goodwill and other long-lived assets); write-downs of inventory to net realizable value; equity-based compensation expense; post-employment, post-retirement and other employee benefit liabilities; valuation allowances for deferred tax assets; reserves for contingencies and litigation; and the fair value and accounting treatment of financial instruments including derivative instruments. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances. Accordingly, actual results may differ significantly from these estimates under different assumptions or conditions.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In April 2015, the Financial Accounting Standards Board ("FASB") issued an Accounting Standards Update, Interest-Imputation of Interest, which simplifies presentation of debt issuance costs. The new standard requires that debt issuance costs be presented in the balance sheet as a direct deduction from the carrying amount of debt liability, consistent with debt discounts or premiums. The new standard will be effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within fiscal years beginning after December 15, 2016. Early adoption of the amendments in this Update is permitted for financial statements that have not been previously issued. We have elected to adopt the standard early and have presented debt issuance costs as a direct deduction from the carrying amount of debt on our Balance Sheets as of March 31, 2015 and December 31, 2014.

Earnings Per Share (Tables)

3 Months Ended

Mar. 31, 2015

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Earnings Per Share



	Three Months Ended March 31,
	2015			2014
Net income	$	14,823		$	18,371
Less: net income allocated to outstanding restricted stockholders	(46		)	(42		)
Net income allocated to common stockholders	$	14,777		$	18,329
Weighted-average common stock
Outstanding	53,416			53,505
Outstanding assuming dilution	53,869			54,054

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

The weighted-average stock options (in thousands) that are antidilutive and are therefore excluded from the calculation of diluted earnings per common share are:



	Three Months Ended March 31,
	2015	2014
Weighted-average outstanding stock options excluded	306	—

Capital Structure and Accumulated Comprehensive Income (Tables)

3 Months Ended

Mar. 31, 2015

Equity [Abstract]

Schedule of Quarterly Cash Dividends

In 2015, our Board of Directors declared quarterly cash dividends as follows:



Dividends per Common Share		Declaration Date	Record Date	Payable Date
$	0.125	February 12, 2015	March 16, 2015	April 3, 2015

Changes in Accumulated Other Comprehensive Income

The following table presents the changes in accumulated other comprehensive income by component during the three months ended March 31, 2015:



	For the Three Months Ended March 31, 2015
	Unrealized gain/(loss) on cash flow hedges			Unrealized gain/(loss) on short-term investments			Pension and other post-retirement benefits liability			Total
Beginning Balance	$	(134	)	$	(41	)	$	(19,643	)	$	(19,818	)
Other comprehensive income (loss) before reclassifications	(3		)	35			(856		)	(824		)
Amounts reclassed from accumulated other comprehensive income	6			—			477			483
Ending Balance	$	(131	)	$	(6	)	$	(20,022	)	$	(20,159	)

Business Combination (Tables)

3 Months Ended

Mar. 31, 2015

Business Combinations [Abstract]

Schedule of Purchase Price Allocation



Accounts receivable	$	6,898
Inventory	2,534
Other current assets	174
Fixed assets	73,138
Deferred tax assets (net)	13,966
Accounts payable, accrued expenses and other liabilities	(4,389		)
Net tangible assets acquired	92,321
Customer relationships	1,274
Trade Name	4,478
Goodwill	244
Purchase price, net of cash acquired	$	98,317

Schedule of Intangible Assets Acquired as Part of Business Combination

The value of acquired intangible assets and the related estimated useful lives consist of the following:



	Estimated Useful Lives	Value
Customer relationships	15 years	$	1,274
Trade name	Indefinite	4,478
Total intangible assets		$	5,752

Schedule of Pro Forma Financial Information



	Three Months Ended March 31, 2015
Sales	$	188,509
Net income	$	18,417
Basic earnings per share	$	0.34
Diluted earnings per share	$	0.34

Property, Plant and Mine Development (Tables)

3 Months Ended

Mar. 31, 2015

Property, Plant and Equipment [Abstract]

Schedule of Property, Plant and Mine Development

At March 31, 2015 and December 31, 2014, property, plant and mine development consisted of the following:



	March 31, 2015			December 31, 2014
Mining property and mine development	$	197,824		$	197,824
Asset retirement cost	9,559			9,559
Land	28,443			28,443
Land improvements	35,420			35,322
Buildings	47,198			47,149
Machinery and equipment	331,604			323,618
Furniture and fixtures	1,599			1,599
Construction-in-progress	83,269			78,997
	734,916			722,511
Accumulated depletion, depreciation and amortization	(169,579		)	(156,756		)
Total property, plant and mine development, net	$	565,337		$	565,755

Debt (Tables)

3 Months Ended

Mar. 31, 2015

Debt Disclosure [Abstract]

Schedule of Debt

At March 31, 2015 and December 31, 2014, debt consisted of the following:



	March 31, 2015			December 31, 2014
Senior secured credit facility:
Revolver expiring July 23, 2018 (4.75% at March 31, 2015 and December 31, 2014)	$	—		$	—
Term loan facility—final maturity July 23, 2020 (4% - 5.25% at March 31, 2015 and December 31, 2014)	503,100			504,375
Less: Unamortized original issue discount	(1,983		)	(2,078		)
Less: Unamortized debt issuance cost	(6,923		)	(7,211		)
Total debt	494,194			495,086
Less: current portion	(3,321		)	(3,329		)
Total long-term portion of debt	$	490,873		$	491,757

Schedule of Contractual Maturities of Debt

At March 31, 2015, contractual maturities of long-term debt are as follows:



2015	$	3,825
2016	5,100
2017	5,100
2018	5,100
2019	5,100
Thereafter	478,875
	$	503,100

Short-Term Investments (Tables)

3 Months Ended

Mar. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Summary of Available-for-Sale Short-Term Investments

The following table summarizes our available-for-sale short-term investments as of March 31, 2015:



	Aggregate Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Money market mutual funds	$	995	$	—	$	—		$	995
Cash	1		—		—			1
Fixed income securities:
Certificates of deposit	28,767		2		(7		)	28,762
Commercial paper	10,186		12		(1		)	10,197
Corporate notes and bonds	12,539		—		(7		)	12,532
Government agencies	16,673		6		(8		)	16,671
U.S. Treasuries	2,152		—		(3		)	2,149
Variable Rate Demand Obligations	3,946		—		—			3,946
Total available-for-sale investments	$	75,259	$	20	$	(26	)	$	75,253

Pension and Post-Retirement Benefits (Tables)

3 Months Ended

Mar. 31, 2015

Compensation and Retirement Disclosure [Abstract]

Summarizes Information about Pension and Post-Retirement Benefit Plans



	Three Months Ended March 31,
	2015			2014
Service cost	$	324		$	269
Interest cost	1,203			1,143
Expected return on plan assets	(1,375		)	(1,255		)
Net amortization and deferral	666			238
Net pension benefit costs	$	818		$	395



	Three Months Ended March 31,
	2015			2014
Service cost	$	44		$	45
Interest cost	277			257
Expected return on plan assets	(1		)	(1		)
Net amortization and deferral	96			—
Net post-retirement costs	$	416		$	301

Segment Reporting (Tables)

3 Months Ended

Mar. 31, 2015

Segment Reporting [Abstract]

Presentation of Sales and Segment Contribution Margin for Reporting Segments and Other Operating Results



	Three Months Ended March 31,
	2015			2014
Sales:
Oil & Gas Proppants	$	148,753		$	130,584
Industrial & Specialty Products	55,205			49,511
Total Sales	203,958			180,095
Segment contribution margin:
Oil & Gas Proppants	52,195			41,628
Industrial & Specialty Products	15,456			13,187
Total segment contribution margin	67,651			54,815
Operating activities excluded from segment cost of goods sold	(2,346		)	(1,490		)
Selling, general and administrative	(26,961		)	(15,445		)
Depreciation, depletion and amortization	(13,243		)	(9,589		)
Interest expense	(6,836		)	(3,808		)
Other income, net, including interest income	11			38
Income before income taxes	$	18,276		$	24,521

Earnings Per Share - Schedule of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 14,823	$ 18,371
Less: net income allocated to outstanding restricted stockholders	(46)	(42)
Net income allocated to common stockholders	$ 14,777	$ 18,329
Weighted-average common stock
Outstanding (in shares)	53,416	53,505
Outstanding assuming dilution (in shares)	53,869	54,054

Capital Structure and Accumulated Comprehensive Income (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Capital Structure And Accumulated Comprehensive Income (Loss)
Common stock outstanding (shares)	53,374,963	53,733,092
Preferred stock issued (shares)	0	0
Preferred stock outstanding (shares)	0	0
Authorization to repurchase common stock	$ 50,000,000
Repurchase of common stock (shares)	706,093
Average price per common share of repurchase common stock (in USD per share)	$ 23.83
Remaining authorized repurchase of common stock amount	$ 33,200,000
Common Stock
Capital Structure And Accumulated Comprehensive Income (Loss)
Common stock authorized (shares)	500,000,000
Common stock, par value	$ 0.01
Common stock issued (shares)	53,374,963	53,733,092
Preferred Stock
Capital Structure And Accumulated Comprehensive Income (Loss)
Preferred stock authorized (shares)	10,000,000
Preferred stock, par value	$ 0.01

Capital Structure and Accumulated Comprehensive Income - Schedule of Quarterly Cash Dividends (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Feb. 12, 2015
Equity [Abstract]
Dividends per common share		$ 0.125
Declaration date	Feb. 12, 2015
Record date	Mar. 16, 2015
Payable date	Apr. 03, 2015

Capital Structure and Accumulated Comprehensive Income - Changes in Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (19,818)
Other comprehensive income (loss) before reclassifications	(824)
Amounts reclassed from accumulated other comprehensive income	483
Ending Balance	(20,159)
Unrealized Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(134)
Other comprehensive income (loss) before reclassifications	(3)
Amounts reclassed from accumulated other comprehensive income	6
Ending Balance	(131)
Unrealized Gain/(Loss) on Short-Term Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(41)
Other comprehensive income (loss) before reclassifications	35
Amounts reclassed from accumulated other comprehensive income	0
Ending Balance	(6)
Pension and Other Postretirement Benefits Liability
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(19,643)
Other comprehensive income (loss) before reclassifications	(856)
Amounts reclassed from accumulated other comprehensive income	477
Ending Balance	$ (20,022)

Business Combination (Details) (USD $)			0 Months Ended
Business Combination (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Jul. 31, 2014 Cadre Services, Inc.	Jul. 31, 2014 Cadre Services, Inc.
Business Acquisition
Total purchase price			$ 98,300,000
Goodwill	68,647,000	68,647,000		244,000
Goodwill expected to be tax deductible				$ 0

Business Combination - Schedule of Purchase Price Allocation (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Jul. 31, 2014 Cadre Services, Inc.	Jul. 31, 2014 Customer Relationships Cadre Services, Inc.	Jul. 31, 2014 Trade Names Cadre Services, Inc.
Business Acquisition
Accounts receivable			$ 6,898
Inventory			2,534
Other current assets			174
Fixed assets			73,138
Deferred tax assets (net)			13,966
Accounts payable, accrued expenses and other liabilities			(4,389)
Net tangible assets acquired			92,321
Total intangible assets			5,752	1,274	4,478
Goodwill	68,647	68,647	244
Purchase price, net of cash acquired			$ 98,317

Business Combination - Schedule of Intangible Assets Acquired as Part of Business Combination (Details) (Cadre Services, Inc., USD $) In Thousands, unless otherwise specified	0 Months Ended
	Jul. 31, 2014	Jul. 31, 2014
Business Acquisition
Total intangible assets	$ 5,752	$ 5,752
Customer Relationships
Business Acquisition
Estimated Useful Lives	15 years
Total intangible assets		1,274
Trade Names
Business Acquisition
Total intangible assets	$ 4,478	$ 4,478

Business Combination - Schedule of Pro Forma Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Business Combinations [Abstract]
Sales	$ 188,509
Net income	$ 18,417
Basic earnings per share (in usd per share)	$ 0.34
Diluted earnings per share (in usd per share)	$ 0.34

Accounts Receivable - Schedule of Accounts Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Receivables [Abstract]
Trade receivables	$ 107,308	$ 128,498
Less: Allowance for doubtful accounts	(13,611)	(10,429)
Net trade receivables	93,697	118,069
Other receivables	2,658	2,812
Total accounts receivable	$ 96,355	$ 120,881

Accounts Receivable - Allowance for Doubtful Accounts (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Allowance for Doubtful Accounts Receivable
Beginning balance	$ 10,429
Bad debt provision	3,183
Write-offs	(1)
Ending balance	$ 13,611

Inventories - Schedule of Inventories (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
Supplies	$ 18,059	$ 17,528
Raw materials and work in process	9,446	12,562
Finished goods	37,530	36,622
Total inventories	$ 65,035	$ 66,712

Property, Plant and Mine Development - Schedule of Property, Plant and Mine Development (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment
Property, plant and mine development	$ 734,916	$ 722,511
Accumulated depletion, depreciation and amortization	(169,579)	(156,756)
Total property, plant and mine development, net	565,337	565,755
Mining Property and Mine Development
Property, Plant and Equipment
Property, plant and mine development	197,824	197,824
Asset Retirement Cost
Property, Plant and Equipment
Property, plant and mine development	9,559	9,559
Land
Property, Plant and Equipment
Property, plant and mine development	28,443	28,443
Land Improvements
Property, Plant and Equipment
Property, plant and mine development	35,420	35,322
Buildings
Property, Plant and Equipment
Property, plant and mine development	47,198	47,149
Machinery and Equipment
Property, Plant and Equipment
Property, plant and mine development	331,604	323,618
Furniture and Fixtures
Property, Plant and Equipment
Property, plant and mine development	1,599	1,599
Construction-in-Progress
Property, Plant and Equipment
Property, plant and mine development	$ 83,269	$ 78,997

Debt (Detail) (USD $)	3 Months Ended
Debt (Detail) (USD $)	Mar. 31, 2015
Short-term Debt
Credit facility consolidated total net leverage ratio	0.0375
Net leverage ratio, credit facility threshold (percentage)	25.00%
Revolving Line-of-Credit
Short-term Debt
Available borrowing base	$ 50,000,000
Amount drawn from borrowing base	0
Amount available for general corporate use under this revolving credit agreement	46,900,000
Letter of Credit
Short-term Debt
Amount allocated for letters of credit	$ 3,100,000

Debt - Schedule of Debt (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Line of Credit Facility
Less: Unamortized debt issuance cost	$ (6,923)	$ (7,211)
Total debt	494,194	495,086
Less: current portion	(3,321)	(3,329)
Total long-term portion of debt	490,873	491,757
Revolving Line-of-Credit
Line of Credit Facility
Total debt	0	0
Credit facility, maturity date	Jul. 23, 2018
Credit facility, interest rate	4.75%	4.75%
Term Loan Facility
Line of Credit Facility
Less: Unamortized original issue discount	(1,983)	(2,078)
Total debt	$ 503,100	$ 504,375
Credit facility, maturity date	Jul. 23, 2020
Minimum \| Term Loan Facility
Line of Credit Facility
Credit facility, interest rate	4.00%	4.00%
Maximum \| Term Loan Facility
Line of Credit Facility
Credit facility, interest rate	5.25%	5.25%

Debt - Schedule of Contractual Maturities of Debt (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Debt Disclosure [Abstract]
2015	$ 3,825
2016	5,100
2017	5,100
2018	5,100
2019	5,100
Thereafter	478,875
Total debt	$ 503,100

Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Beginning balance	$ 11,283	$ 9,378
Payments	0	(782)
Accretion	187	676
Additions and revisions of prior estimates	0	2,011
Ending balance	$ 11,470	$ 11,283

Fair Value Accounting - Schedule of Measure at Fair Value on Recurring Basis (Detail) (Measured at Fair Value on Recurring Basis, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Defined Benefit Plan Disclosure
Short-term investments	$ 75,253
Interest rate derivatives	0
Net asset	75,253
Level 1
Defined Benefit Plan Disclosure
Short-term investments	995
Interest rate derivatives	0
Net asset	995
Level 2
Defined Benefit Plan Disclosure
Short-term investments	74,258
Interest rate derivatives	0
Net asset	$ 74,258

Short-Term Investments - Schedule of Available-for-Sale Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities
Aggregate Cost	$ 75,259
Gross Unrealized Gains	20
Gross Unrealized Losses	(26)
Fair Value	75,253	75,143
Money Market Mutual Funds
Schedule of Available-for-sale Securities
Aggregate Cost	995
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	995
Cash
Schedule of Available-for-sale Securities
Aggregate Cost	1
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	1
Certificates Of Deposit
Schedule of Available-for-sale Securities
Aggregate Cost	28,767
Gross Unrealized Gains	2
Gross Unrealized Losses	(7)
Fair Value	28,762
Commercial Paper
Schedule of Available-for-sale Securities
Aggregate Cost	10,186
Gross Unrealized Gains	12
Gross Unrealized Losses	(1)
Fair Value	10,197
Corporate Notes And Bonds
Schedule of Available-for-sale Securities
Aggregate Cost	12,539
Gross Unrealized Gains	0
Gross Unrealized Losses	(7)
Fair Value	12,532
Government Agencies
Schedule of Available-for-sale Securities
Aggregate Cost	16,673
Gross Unrealized Gains	6
Gross Unrealized Losses	(8)
Fair Value	16,671
US Treasuries
Schedule of Available-for-sale Securities
Aggregate Cost	2,152
Gross Unrealized Gains	0
Gross Unrealized Losses	(3)
Fair Value	2,149
Variable Rate Demand Obligations
Schedule of Available-for-sale Securities
Aggregate Cost	3,946
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 3,946

Commitments and Contingencies (Detail) (USD $)	3 Months Ended
Commitments and Contingencies (Detail) (USD $)	Mar. 31, 2015 claim	Mar. 31, 2014	Dec. 31, 2014
Insurance [Abstract]
Expenses related to operating leases and rental agreements	$ 10,000,000	$ 7,100,000
Capital lease obligations	0
New claims filed	0
Number of active products liability claims outstanding	75
Third party products claims liability under insurance in other assets	311,000		311,000
Third party products claims liability under insurance in other long-term obligations	1,600,000		1,600,000
Selling, General and Administrative Expense
Loss Contingencies
Litigation settlement expense	$ 7,600,000

Commitments and Contingencies - Schedule of Future Minimum Annual Commitments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Operating Leases
2015	$ 31,851
2016	45,069
2017	42,675
2018	41,026
2019	34,485
Thereafter	103,523
Total future lease commitments	298,629
Minimum Purchase Commitments
2015	29,917
2016	30,464
2017	19,871
2018	15,754
2019	10,000
Thereafter	16,356
Total future purchase commitments	$ 122,362

Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Loss Contingencies
Discrete tax benefit related to unfavorable ruling	$ 2.9
Effective income tax rate	19.00%	25.00%
Effective income tax rate without discrete tax benefit	0.25
Selling, General and Administrative Expense
Loss Contingencies
Litigation settlement expense	$ 7.6

Pension and Post-Retirement Benefits (Detail) (USD $)	3 Months Ended
Pension and Post-Retirement Benefits (Detail) (USD $)	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits
Defined Benefit Plan Disclosure
Contributions to plan by employer	$ 0	$ 800,000
Expected contributions in current fiscal year	1,700,000
Post-retirement Benefits
Defined Benefit Plan Disclosure
Expected contributions in current fiscal year	$ 1,700,000

Pension and Post-Retirement Benefits - Summarizes Information about Pension and Post-Retirement Benefit Plans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 324	$ 269
Interest cost	1,203	1,143
Expected return on plan assets	(1,375)	(1,255)
Net amortization and deferral	666	238
Net pension benefit costs	818	395
Post-retirement Benefits
Defined Benefit Plan Disclosure
Service cost	44	45
Interest cost	277	257
Expected return on plan assets	(1)	(1)
Net amortization and deferral	96	0
Net pension benefit costs	$ 416	$ 301

Obligations Under Guarantees (Detail) (USD $)	3 Months Ended
Obligations Under Guarantees (Detail) (USD $)	Mar. 31, 2015 railroad_car
Travelers Casualty and Surety Company \| Surety Bonds
Loss Contingencies
Surety bonds outstanding	$ 8,500,000
Travelers Casualty and Surety Company \| Reclamation Bonds
Loss Contingencies
Bonds related to reclamation requirements	8,200,000
Kanawha Rail Corporation \| Leased Railroad Hopper Cars
Loss Contingencies
Number of railroad cars	199
Payment of monthly rent	$ 66,000

Segment Reporting (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 Product Segment	Dec. 31, 2014
Segment Reporting Information
Number of reportable segments	2
Number of products in Industrial & Specialty segment (over 260)	250
Goodwill	$ 68,647	$ 68,647
Industrial & Specialty Products segment description	Over 250 products and materials used in a variety of industries including, container glass, fiberglass, specialty glass, flat glass, building products, fillers and extenders, foundry products, chemicals, recreation products and filtration products.
Oil & Gas Proppants
Segment Reporting Information
Goodwill	47,900
Industrial & Specialty Products
Segment Reporting Information
Goodwill	$ 20,700

Segment Reporting - Presentation of Sales and Segment Contribution Margin for Reporting Segments and Other Operating Results (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information
Total Sales	$ 203,958	$ 180,095
Total segment contribution margin	67,651	54,815
Operating activities excluded from segment cost of goods sold	(2,346)	(1,490)
Selling, general and administrative	(26,961)	(15,445)
Depreciation, depletion and amortization	(13,243)	(9,589)
Interest expense	(6,836)	(3,808)
Other income, net, including interest income	11	38
Income before income taxes	18,276	24,521
Operating Segments \| Oil & Gas Proppants
Segment Reporting Information
Total Sales	148,753	130,584
Total segment contribution margin	52,195	41,628
Operating Segments \| Industrial & Specialty Products
Segment Reporting Information
Total Sales	55,205	49,511
Total segment contribution margin	$ 15,456	$ 13,187

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	NOTE Q—SUBSEQUENT EVENTS On April 3, 2015 we paid a cash dividend of $0.125 per share to common stockholders of record on March 16, 2015, which had been declared by our Board of Directors on February 12, 2015.

Subsequent Events (Details) (USD $)	3 Months Ended	0 Months Ended
Subsequent Events (Details) (USD $)	Mar. 31, 2015	Apr. 03, 2015 Subsequent Event
Subsequent Event
Dividends, Common Stock, Cash	$ 6,691,000	$ 0.125

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2015
Statement of Stockholders' Equity [Abstract]
Common stock cash dividend declared, per share	$ 0.125

Earnings Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) (Employee Stock Options) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Employee Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted-average outstanding stock options excluded	306	0

Asset Retirement Obligations (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation	$ 11,470	$ 11,283	$ 9,378

Short-Term Investments (Detail) (USD $)	3 Months Ended
Short-Term Investments (Detail) (USD $)	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Impairment charges	$ 0