Document and Entity Information	6 Months Ended
Document and Entity Information	Jun. 30, 2015	Jul. 27, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2
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		53,388,125

Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015	Dec. 31, 2014
Current Assets:
Cash and cash equivalents	$ 251,488	$ 267,281
Short-term investments	70,740	75,143
Accounts receivable, net	77,777	120,881
Inventories, net	64,183	66,712
Prepaid expenses and other current assets	9,658	9,267
Deferred income taxes, net	21,472	22,295
Income tax deposits	3,979	746
Total current assets	499,297	562,325
Property, plant and mine development, net	567,197	565,755
Goodwill	68,647	68,647
Trade names	14,914	14,914
Customer relationships, net	6,700	6,984
Other assets	17,915	12,317
Total assets	1,174,670	1,230,942
Current Liabilities:
Book overdraft	3,833	4,215
Accounts payable	53,815	85,781
Dividends payable	6,754	6,805
Accrued liabilities	14,431	17,911
Accrued interest	58	60
Current portion of long-term debt	3,324	3,329
Deferred revenue	26,771	26,771
Total current liabilities	108,986	144,872
Long-term debt	490,041	491,757
Deferred revenue	55,506	64,722
Liability for pension and other post-retirement benefits	53,765	59,932
Deferred income taxes, net	44,648	49,749
Other long-term obligations	17,725	16,094
Total liabilities	770,671	827,126
Stockholders’ Equity:
Common stock	539	539
Additional paid-in capital	191,042	191,086
Retained earnings	243,934	232,551
Treasury stock, at cost	(15,937)	(542)
Accumulated other comprehensive loss	(15,579)	(19,818)
Total stockholders’ equity	403,999	403,816
Total liabilities and stockholders’ equity	$ 1,174,670	$ 1,230,942

Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Sales	$ 147,511	$ 205,801	$ 351,469	$ 385,896
Cost of goods sold (excluding depreciation, depletion and amortization)	117,200	132,417	255,853	259,187
Operating expenses
Selling, general and administrative	6,575	19,267	33,536	34,712
Depreciation, depletion and amortization	13,695	10,341	26,938	19,930
Total operating expenses	20,270	29,608	60,474	54,642
Operating income	10,041	43,776	35,142	72,067
Other (expense)/income
Interest expense	(6,249)	(4,013)	(13,085)	(7,821)
Other (expense)/income, net, including interest income	(181)	221	(170)	259
Total other (expenses) income	(6,430)	(3,792)	(13,255)	(7,562)
Income before income taxes	3,611	39,984	21,887	64,505
Income tax benefit/(expense)	6,342	(11,330)	2,889	(17,480)
Net income	$ 9,953	$ 28,654	$ 24,776	$ 47,025
Earnings per share:
Basic (in usd per share)	$ 0.19	$ 0.53	$ 0.46	$ 0.88
Diluted (in usd per share)	$ 0.18	$ 0.53	$ 0.46	$ 0.87
Weighted Average Number of Shares Outstanding, Basic	53,303	53,733	53,361	53,619
Weighted Average Number of Shares Outstanding, Diluted	53,857	54,262	53,864	54,163
Common stock cash dividend declared, per share	$ 0.13	$ 0.13	$ 0.25	$ 0.25

Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 9,953	$ 28,654	$ 24,776	$ 47,025
Other comprehensive income:
Unrealized gain (loss) on derivatives (net of tax of $6 and ($22) for the three months ended June 30, 2015 and 2014, respectively, and $8 and ($34) for the six months ended June 30, 2015 and 2014, respectively)	9	(34)	12	(53)
Unrealized gain (loss) on investments (net of tax of $8 and ($5) for the three months ended June 30, 2015 and 2014, respectively, and $30 and $14 for the six months ended June 30, 2015 and 2014, respectively)	14	(6)	49	23
Pension and other post-retirement benefits liability adjustment (net of tax of $2,823 and $95 for the three months ended June 30, 2015 and 2014, respectively, and $2,588 and $190 for the six months ended June 30, 2015 and 2014, respectively)	4,557	149	4,178	298
Comprehensive income	$ 14,533	$ 28,763	$ 29,015	$ 47,293

Condensed Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2015	Jun. 30, 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)	$ 12	$ (53)
Unrealized gain (loss) on investments (net of tax of $22 and $19 for the three months ended March 31, 2015 and 2014, respectively)	49	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)	$ 4,178	$ 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	24,776,000				24,776,000
Unrealized gain on derivatives	12,000					12,000
Unrealized gain on short-term investments	49,000					49,000
Pension and post-retirement liability	4,178,000					4,178,000
Cash dividend declared ($0.25 per share)	(13,393,000)				(13,393,000)
Common stock-based compensation plans activity:	(89,000)			(89,000)
Equity-based compensation	264,000			264,000
Unrealized gain on short-term investments	363,000		582,000	(219,000)
Pension and post-retirement liability	(722,000)	0	(722,000)
Repurchase of common stock	(15,255,000)		(15,255,000)
Balance at June 30, 2015 at Jun. 30, 2015	$ 403,999,000	$ 539,000	$ (15,937,000)	$ 191,042,000	$ 243,934,000	$ (15,579,000)

Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Statement of Cash Flows [Abstract]
Proceeds from Sale and Maturity of Available-for-sale Securities	$ 4,593	$ 0
Operating activities:
Net income	24,776	47,025
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	26,938	19,930
Debt issuance amortization	703	439
Original issue discount amortization	192	131
Deferred income taxes	(6,903)	2,042
Deferred revenue	(9,216)	0
(Gain)/loss on disposal of property, plant and equipment	811	79
Equity-based compensation	(89)	3,383
Excess tax benefit from equity-based compensation	(264)	(2,801)
Other	(6,274)	3,184
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	43,451	(33,926)
Inventories	2,529	5,562
Prepaid expenses and other current assets	(445)	(2,659)
Income taxes	(3,233)	(3,310)
Accounts payable and accrued liabilities	(35,446)	17,647
Liability for pension and other post-retirement benefits	927	(1,504)
Net cash provided by operating activities	38,457	55,222
Investing activities:
Capital expenditures	(27,128)	(18,011)
Proceeds from sale of property, plant and equipment	77	0
Net cash used in investing activities	(22,458)	(18,011)
Financing activities:
Dividends paid	(13,444)	(13,402)
Repurchase of common stock	(15,255)	0
Proceeds from options exercised	363	4,710
Excess tax benefit from equity-based compensation	264	2,801
Tax payments related to shares withheld for vested restricted stock	(722)	(534)
Repayment of long-term debt	(2,550)	(1,875)
Change in book overdraft	(384)	(1,193)
Financing fees	(64)	0
Net cash used in financing activities	(31,792)	(9,493)
Net increase/(decrease) in cash and cash equivalents	(15,793)	27,718
Cash and cash equivalents, beginning of period	267,281	78,256
Cash and cash equivalents, end of period	251,488	105,974
Cash paid during the period for:
Interest	10,977	7,668
Taxes	$ 6,984	$ 18,920

Summary of Significant Accounting Policies	6 Months Ended
Summary of Significant Accounting Policies	Jun. 30, 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 June 30, 2015; the Income Statements for the three and six months ended June 30, 2015 and 2014; the Condensed Consolidated Statements of Comprehensive Income for the three and six months ended June 30, 2015 and 2014; the Condensed Consolidated Statements of Stockholders' Equity for the six months ended June 30, 2015; the Cash Flows for the six months ended June 30, 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 June 30, 2015 and December 31, 2014.

Capital Structure and Accumulated Comprehensive Income

6 Months Ended

Jun. 30, 2015

Equity [Abstract]

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 53,383,613 shares of common stock issued and outstanding at June 30, 2015. As of June 30, 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
$	0.125	May 8, 2015	June 15, 2015	July 6, 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 June 30, 2015. At present, we have no plans to issue any preferred stock.

Employee Stock Awards

We grant stock options, restricted stock, restricted stock units and performance share units to our employees and directors under the Amended and Restated U.S. Silica Holdings, Inc. 2011 Incentive Compensation Plan. The weighted-average stock options that are antidilutive and are therefore excluded from the calculation of our diluted earnings per common share are:



	Three Months Ended June 30,		Six Months Ended June 30,
	2015	2014	2015	2014
Weighted-average outstanding stock options excluded	450	—	371	—

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 June 30, 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 June 30, 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 six months ended June 30, 2015:



	For the Six Months Ended June 30, 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		)	49			3,225			3,271
Amounts reclassed from accumulated other comprehensive income	15			—			953			968
Ending Balance	$	(122	)	$	8		$	(15,465	)	$	(15,579	)

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

Business Combination

6 Months Ended

Jun. 30, 2015

Business Combinations [Abstract]

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 June 30, 2014		Six Months Ended June 30, 2014
Sales	$	218,154	$	406,663
Net income	31,818		49,949
Basic earnings per share	0.59		0.93
Diluted earnings per share	$	0.59	$	0.92

Property, Plant and Mine Development

6 Months Ended

Jun. 30, 2015

Property, Plant and Equipment [Abstract]

Property, Plant and Mine Development

At June 30, 2015 and December 31, 2014, property, plant and mine development consisted of the following:



	June 30, 2015			December 31, 2014
Mining property and mine development	$	223,086		$	197,824
Asset retirement cost	10,971			9,559
Land	29,846			28,443
Land improvements	36,874			35,322
Buildings	49,791			47,149
Machinery and equipment	350,479			323,618
Furniture and fixtures	1,647			1,599
Construction-in-progress	47,376			78,997
	750,070			722,511
Accumulated depletion, depreciation and amortization	(182,873		)	(156,756		)
Total property, plant and mine development, net	$	567,197		$	565,755

The amount of interest costs capitalized in property, plant and mine development was $281 and $474 for the six months ended June 30, 2015 and 2014, respectively.

Debt

6 Months Ended

Jun. 30, 2015

Debt Disclosure [Abstract]

Debt

At June 30, 2015 and December 31, 2014, debt consisted of the following:



	June 30, 2015			December 31, 2014
Senior secured credit facility:
Revolver expiring July 23, 2018 (4.75% at June 30, 2015 and December 31, 2014)	$	—		$	—
Term loan facility—final maturity July 23, 2020 (4% - 4.5% at June 30, 2015 and 4% - 5.25% at December 31, 2014)	501,825			504,375
Less: Unamortized original issue discount	(1,887		)	(2,078		)
Less: Unamortized debt issuance cost	(6,573		)	(7,211		)
Total debt	493,365			495,086
Less: current portion	(3,324		)	(3,329		)
Total long-term portion of debt	$	490,041		$	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 June 30, 2015, leaving $46.9 million available under the Revolver.

Debt Maturities

At June 30, 2015, contractual maturities of long-term debt are as follows:



2015	$	2,550
2016	5,100
2017	5,100
2018	5,100
2019	5,100
Thereafter	478,875
	$	501,825

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 June 30, 2015, we are in compliance with all covenants in accordance with our senior secured credit facility.

Asset Retirement Obligations

6 Months Ended

Jun. 30, 2015

Asset Retirement Obligation Disclosure [Abstract]

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 June 30, 2015, we had recorded a liability of $13.1 million in other long-term obligations related to our asset retirement obligation. Changes in the asset retirement obligation during the six months ended June 30, 2015, are as follows:



	June 30, 2015
Beginning balance	$	11,283
Payments	—
Accretion	390
Additions and revisions of prior estimates	1,412
Ending balance	$	13,085

Fair Value Accounting

6 Months Ended

Jun. 30, 2015

Fair Value Disclosures [Abstract]

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 June 30, 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, approximate 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 June 30, 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 June 30, 2015 of those assets that we measure at fair value on a recurring basis:



	Level 1		Level 2		Total
Short-term investments	$	980	$	69,760	$	70,740
Interest rate derivatives	—		—		—
Net asset	$	980	$	69,760	$	70,740

Short-Term Investments

6 Months Ended

Jun. 30, 2015

Investments, Debt and Equity Securities [Abstract]

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 June 30, 2015:



	Aggregate Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Money market mutual funds	$	980	$	—	$	—		$	980
Fixed income securities:
Certificates of deposit	24,650		7		—			24,657
Commercial paper	10,175		10		—			10,185
Corporate notes and bonds	12,498		—		(5		)	12,493
Government agencies	16,662		13		(9		)	16,666
U.S. Treasuries	2,148		—		—			2,148
Variable Rate Demand Obligations	3,611		—		—			3,611
Total available-for-sale investments	$	70,724	$	30	$	(14	)	$	70,740

As of June 30, 2015, we considered any 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 June 30, 2015, we did not recognize any impairment charges.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2015

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Future Minimum Annual Commitments at June 30, 2015:



	Operating Leases		Minimum Purchase Commitments
2015	$	22,481	$	19,384
2016	45,034		31,661
2017	42,671		21,529
2018	40,961		17,442
2019	34,415		11,147
Thereafter	104,921		16,778
Total future lease and purchase commitments	$	290,483	$	117,941

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 $11.7 million and $8.2 million for the three months ended June 30, 2015 and 2014, respectively, and $21.7 million and $15.3 million for the six months ended June 30, 2015 and 2014, respectively. As of June 30, 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 June 30, 2015, no new claims were brought against U.S. Silica. As of June 30, 2015, there were 77 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 June 30, 2015, and December 31, 2014 other non-current assets included $0.3 million for insurance for third-party products liability claims and other long-term obligations included $1.4 million in third-party products claims liability.

Additionally, during the three months ended March 31, 2015, we 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. The matter was settled and the settlement amount of $6.5 million was paid on June 9, 2015, which was included in selling, general and administrative expense in our Income Statement for the six months ended June 30, 2015.

Income Taxes	6 Months Ended
Income Taxes	Jun. 30, 2015
Income Tax Disclosure [Abstract]
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 six months ended June 30, 2015, we recorded a discrete tax benefit of $2.9 million, which relates to the arbitration ruling described in Note K - Commitments and Contingencies. The effective tax rate was (13)% and 27% for six months ended June 30, 2015 and 2014, respectively. The tax rate for the six months ending June 30, 2015 would have been 0% 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

6 Months Ended

Jun. 30, 2015

Compensation and Retirement Disclosure [Abstract]

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 and six months ended June 30, 2015 and 2014 are as follows:



	Three Months Ended June 30,						Six Months Ended June 30,
	2015			2014			2015			2014
Service cost	$	324		$	270		$	647		$	539
Interest cost	1,203			1,142			2,406			2,285
Expected return on plan assets	(1,375		)	(1,255		)	(2,749		)	(2,510		)
Net amortization and deferral	666			238			1,333			476
Net pension benefit costs	$	818		$	395		$	1,637		$	790

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 and six months ended June 30, 2015 and 2014 are as follows:



	Three Months Ended June 30,						Six Months Ended June 30,
	2015			2014			2015			2014
Service cost	$	44		$	45		$	88		$	90
Interest cost	277			257			554			514
Expected return on plan assets	(1		)	(1		)	(2		)	(2		)
Net amortization and deferral	96			—			192			—
Net post-retirement costs	$	416		$	301		$	832		$	602

The weighted average discount rate used to determine the projected pension and post-retirement obligations was updated during the three months ended June 30, 2015, and was increased from 4.1% at December 31, 2014 to 4.5% at June 30, 2015. We contributed $1.0 million and $1.9 million to the qualified pension plan during the three months ended June 30, 2015 and 2014, respectively, and $2.6 million during the six months ended June 30, 2014. We made no contributions to the plan during the preceding three month period ending March 31, 2015. Total expected employer funding contributions during the fiscal year ending December 31, 2015 are $2.0 million for the pension plan and $1.4 million for the post-retirement medical and life plan.

Obligations under Guarantees	6 Months Ended
Obligations under Guarantees	Jun. 30, 2015
Guarantees [Abstract]
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 June 30, 2015, Travelers had $9.9 million in bonds outstanding for us. The majority of these bonds, $9.5 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.

Segment Reporting

6 Months Ended

Jun. 30, 2015

Segment Reporting [Abstract]

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 260 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 and six months ended June 30, 2015 and 2014:



	Three Months Ended June 30,						Six Months Ended June 30,
	2015			2014			2015			2014
Sales:
Oil & Gas Proppants	$	90,855		$	149,331		$	239,607		$	279,915
Industrial & Specialty Products	56,656			56,470			111,862			105,981
Total Sales	147,511			205,801			351,469			385,896
Segment contribution margin:
Oil & Gas Proppants	13,257			57,060			65,451			98,688
Industrial & Specialty Products	19,531			17,615			34,987			30,802
Total segment contribution margin	32,788			74,675			100,438			129,490
Operating activities excluded from segment cost of goods sold	(2,477		)	(1,291		)	(4,822		)	(2,781		)
Selling, general and administrative	(6,575		)	(19,267		)	(33,536		)	(34,712		)
Depreciation, depletion and amortization	(13,695		)	(10,341		)	(26,938		)	(19,930		)
Interest expense	(6,249		)	(4,013		)	(13,085		)	(7,821		)
Other (expense)/income, net, including interest income	(181		)	221			(170		)	259
Income before income taxes	$	3,611		$	39,984		$	21,887		$	64,505

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)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 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 June 30, 2015; the Income Statements for the three and six months ended June 30, 2015 and 2014; the Condensed Consolidated Statements of Comprehensive Income for the three and six months ended June 30, 2015 and 2014; the Condensed Consolidated Statements of Stockholders' Equity for the six months ended June 30, 2015; the Cash Flows for the six months ended June 30, 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 June 30, 2015 and December 31, 2014.

Capital Structure and Accumulated Comprehensive Income (Tables)

6 Months Ended

Jun. 30, 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
$	0.125	May 8, 2015	June 15, 2015	July 6, 2015

Changes in Accumulated Other Comprehensive Income

The following table presents the changes in accumulated other comprehensive income by component during the six months ended June 30, 2015:



	For the Six Months Ended June 30, 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		)	49			3,225			3,271
Amounts reclassed from accumulated other comprehensive income	15			—			953			968
Ending Balance	$	(122	)	$	8		$	(15,465	)	$	(15,579	)

Capital Structure and Accumulated Comprehensive Income Untidilutive options excluded from diluted EPS (Tables)

6 Months Ended

Jun. 30, 2015

Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]

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

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



	Three Months Ended June 30,		Six Months Ended June 30,
	2015	2014	2015	2014
Weighted-average outstanding stock options excluded	450	—	371	—

Business Combination (Tables)

6 Months Ended

Jun. 30, 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 June 30, 2014		Six Months Ended June 30, 2014
Sales	$	218,154	$	406,663
Net income	31,818		49,949
Basic earnings per share	0.59		0.93
Diluted earnings per share	$	0.59	$	0.92

Property, Plant and Mine Development (Tables)

6 Months Ended

Jun. 30, 2015

Property, Plant and Equipment [Abstract]

Schedule of Property, Plant and Mine Development

At June 30, 2015 and December 31, 2014, property, plant and mine development consisted of the following:



	June 30, 2015			December 31, 2014
Mining property and mine development	$	223,086		$	197,824
Asset retirement cost	10,971			9,559
Land	29,846			28,443
Land improvements	36,874			35,322
Buildings	49,791			47,149
Machinery and equipment	350,479			323,618
Furniture and fixtures	1,647			1,599
Construction-in-progress	47,376			78,997
	750,070			722,511
Accumulated depletion, depreciation and amortization	(182,873		)	(156,756		)
Total property, plant and mine development, net	$	567,197		$	565,755

Debt (Tables)

6 Months Ended

Jun. 30, 2015

Debt Disclosure [Abstract]

Schedule of Debt

At June 30, 2015 and December 31, 2014, debt consisted of the following:



	June 30, 2015			December 31, 2014
Senior secured credit facility:
Revolver expiring July 23, 2018 (4.75% at June 30, 2015 and December 31, 2014)	$	—		$	—
Term loan facility—final maturity July 23, 2020 (4% - 4.5% at June 30, 2015 and 4% - 5.25% at December 31, 2014)	501,825			504,375
Less: Unamortized original issue discount	(1,887		)	(2,078		)
Less: Unamortized debt issuance cost	(6,573		)	(7,211		)
Total debt	493,365			495,086
Less: current portion	(3,324		)	(3,329		)
Total long-term portion of debt	$	490,041		$	491,757

Schedule of Contractual Maturities of Debt

At June 30, 2015, contractual maturities of long-term debt are as follows:



2015	$	2,550
2016	5,100
2017	5,100
2018	5,100
2019	5,100
Thereafter	478,875
	$	501,825

Short-Term Investments (Tables)

6 Months Ended

Jun. 30, 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 June 30, 2015:



	Aggregate Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Money market mutual funds	$	980	$	—	$	—		$	980
Fixed income securities:
Certificates of deposit	24,650		7		—			24,657
Commercial paper	10,175		10		—			10,185
Corporate notes and bonds	12,498		—		(5		)	12,493
Government agencies	16,662		13		(9		)	16,666
U.S. Treasuries	2,148		—		—			2,148
Variable Rate Demand Obligations	3,611		—		—			3,611
Total available-for-sale investments	$	70,724	$	30	$	(14	)	$	70,740

Pension and Post-Retirement Benefits (Tables)

6 Months Ended

Jun. 30, 2015

Compensation and Retirement Disclosure [Abstract]

Summarizes Information about Pension and Post-Retirement Benefit Plans



	Three Months Ended June 30,						Six Months Ended June 30,
	2015			2014			2015			2014
Service cost	$	324		$	270		$	647		$	539
Interest cost	1,203			1,142			2,406			2,285
Expected return on plan assets	(1,375		)	(1,255		)	(2,749		)	(2,510		)
Net amortization and deferral	666			238			1,333			476
Net pension benefit costs	$	818		$	395		$	1,637		$	790



	Three Months Ended June 30,						Six Months Ended June 30,
	2015			2014			2015			2014
Service cost	$	44		$	45		$	88		$	90
Interest cost	277			257			554			514
Expected return on plan assets	(1		)	(1		)	(2		)	(2		)
Net amortization and deferral	96			—			192			—
Net post-retirement costs	$	416		$	301		$	832		$	602

Segment Reporting (Tables)

6 Months Ended

Jun. 30, 2015

Segment Reporting [Abstract]

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



	Three Months Ended June 30,						Six Months Ended June 30,
	2015			2014			2015			2014
Sales:
Oil & Gas Proppants	$	90,855		$	149,331		$	239,607		$	279,915
Industrial & Specialty Products	56,656			56,470			111,862			105,981
Total Sales	147,511			205,801			351,469			385,896
Segment contribution margin:
Oil & Gas Proppants	13,257			57,060			65,451			98,688
Industrial & Specialty Products	19,531			17,615			34,987			30,802
Total segment contribution margin	32,788			74,675			100,438			129,490
Operating activities excluded from segment cost of goods sold	(2,477		)	(1,291		)	(4,822		)	(2,781		)
Selling, general and administrative	(6,575		)	(19,267		)	(33,536		)	(34,712		)
Depreciation, depletion and amortization	(13,695		)	(10,341		)	(26,938		)	(19,930		)
Interest expense	(6,249		)	(4,013		)	(13,085		)	(7,821		)
Other (expense)/income, net, including interest income	(181		)	221			(170		)	259
Income before income taxes	$	3,611		$	39,984		$	21,887		$	64,505

Capital Structure and Accumulated Comprehensive Income (Detail) (USD $)	6 Months Ended
	Jun. 30, 2015	Jun. 30, 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)	53,383,613	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 $)	6 Months Ended
	Jun. 30, 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	6 Months Ended
	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (19,818)
Other comprehensive income (loss) before reclassifications	3,271
Amounts reclassed from accumulated other comprehensive income	968
Ending Balance	(15,579)
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	15
Ending Balance	(122)
Unrealized Gain/(Loss) on Short-Term Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(41)
Other comprehensive income (loss) before reclassifications	49
Amounts reclassed from accumulated other comprehensive income	0
Ending Balance	8
Pension and Other Postretirement Benefits Liability
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(19,643)
Other comprehensive income (loss) before reclassifications	3,225
Amounts reclassed from accumulated other comprehensive income	953
Ending Balance	$ (15,465)

Business Combination (Details) (USD $)	3 Months Ended	6 Months Ended			0 Months Ended
Business Combination (Details) (USD $)	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Jul. 31, 2014 Cadre Services, Inc.	Jul. 31, 2014 Cadre Services, Inc.
Business Acquisition
Sales	$ 218,154,000	$ 406,663,000
Total purchase price					98,300,000
Goodwill			68,647,000	68,647,000		244,000
Goodwill expected to be tax deductible						0
Net income	$ 31,818,000	$ 49,949,000
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 0.59	$ 0.93
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 0.59	$ 0.92

Business Combination - Schedule of Purchase Price Allocation (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 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				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
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	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014
Business Combinations [Abstract]
Sales	$ 218,154	$ 406,663
Net income	$ 31,818	$ 49,949
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 0.59	$ 0.93
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 0.59	$ 0.92

Accounts Receivable - Schedule of Accounts Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015	Dec. 31, 2014
Receivables [Abstract]
Trade receivables	$ 86,817	$ 128,498
Less: Allowance for doubtful accounts	(10,082)	(10,429)
Net trade receivables	76,735	118,069
Other receivables	1,042	2,812
Total accounts receivable	$ 77,777	$ 120,881

Accounts Receivable - Allowance for Doubtful Accounts (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2015
Allowance for Doubtful Accounts Receivable
Beginning balance	$ 10,429
Bad debt provision	(255)
Write-offs	(92)
Ending balance	$ 10,082

Inventories - Schedule of Inventories (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
Supplies	$ 18,964	$ 17,528
Raw materials and work in process	15,829	12,562
Finished goods	29,390	36,622
Total inventories	$ 64,183	$ 66,712

Property, Plant and Mine Development - Schedule of Property, Plant and Mine Development (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment
Property, plant and mine development	$ 750,070	$ 722,511
Accumulated depletion, depreciation and amortization	(182,873)	(156,756)
Total property, plant and mine development, net	567,197	565,755
Mining Property and Mine Development
Property, Plant and Equipment
Property, plant and mine development	223,086	197,824
Asset Retirement Cost
Property, Plant and Equipment
Property, plant and mine development	10,971	9,559
Land
Property, Plant and Equipment
Property, plant and mine development	29,846	28,443
Land Improvements
Property, Plant and Equipment
Property, plant and mine development	36,874	35,322
Buildings
Property, Plant and Equipment
Property, plant and mine development	49,791	47,149
Machinery and Equipment
Property, Plant and Equipment
Property, plant and mine development	350,479	323,618
Furniture and Fixtures
Property, Plant and Equipment
Property, plant and mine development	1,647	1,599
Construction-in-Progress
Property, Plant and Equipment
Property, plant and mine development	$ 47,376	$ 78,997

Debt (Detail) (USD $)	6 Months Ended
Debt (Detail) (USD $)	Jun. 30, 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	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Line of Credit Facility
Less: Unamortized debt issuance cost	$ (6,573)	$ (7,211)
Total debt	493,365	495,086
Less: current portion	(3,324)	(3,329)
Total long-term portion of debt	490,041	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	(1,887)	(2,078)
Total debt	$ 501,825	$ 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	4.50%	5.25%

Debt - Schedule of Contractual Maturities of Debt (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015
Debt Disclosure [Abstract]
2015	$ 2,550
2016	5,100
2017	5,100
2018	5,100
2019	5,100
Thereafter	478,875
Total debt	$ 501,825

Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligation (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2015
Asset Retirement Obligation Disclosure [Abstract]
Beginning balance	$ 11,283
Payments	0
Accretion	390
Additions and revisions of prior estimates	1,412
Ending balance	$ 13,085

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	Jun. 30, 2015
Defined Benefit Plan Disclosure
Short-term investments	$ 70,740
Interest rate derivatives	0
Net asset	70,740
Level 1
Defined Benefit Plan Disclosure
Short-term investments	980
Interest rate derivatives	0
Net asset	980
Level 2
Defined Benefit Plan Disclosure
Short-term investments	69,760
Interest rate derivatives	0
Net asset	$ 69,760

Short-Term Investments - Schedule of Available-for-Sale Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities
Aggregate Cost	$ 70,724
Gross Unrealized Gains	30
Gross Unrealized Losses	(14)
Fair Value	70,740	75,143
Money Market Mutual Funds
Schedule of Available-for-sale Securities
Aggregate Cost	980
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	980
Certificates Of Deposit
Schedule of Available-for-sale Securities
Aggregate Cost	24,650
Gross Unrealized Gains	7
Gross Unrealized Losses	0
Fair Value	24,657
Commercial Paper
Schedule of Available-for-sale Securities
Aggregate Cost	10,175
Gross Unrealized Gains	10
Gross Unrealized Losses	0
Fair Value	10,185
Corporate Notes And Bonds
Schedule of Available-for-sale Securities
Aggregate Cost	12,498
Gross Unrealized Gains	0
Gross Unrealized Losses	(5)
Fair Value	12,493
Government Agencies
Schedule of Available-for-sale Securities
Aggregate Cost	16,662
Gross Unrealized Gains	13
Gross Unrealized Losses	(9)
Fair Value	16,666
US Treasuries
Schedule of Available-for-sale Securities
Aggregate Cost	2,148
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	2,148
Variable Rate Demand Obligations
Schedule of Available-for-sale Securities
Aggregate Cost	3,611
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 3,611

Commitments and Contingencies (Detail) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended
Commitments and Contingencies (Detail) (USD $)	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015 claim	Jun. 30, 2014	Dec. 31, 2014	Mar. 31, 2015 Selling, General and Administrative Expense	Jun. 30, 2015 Selling, General and Administrative Expense
Insurance [Abstract]
Expenses related to operating leases and rental agreements	$ 11,700,000	$ 8,200,000	$ 21,700,000	$ 15,300,000
New claims filed			0
Third party products claims liability under insurance in other assets	300,000		300,000		311,000
Third party products claims liability under insurance in other long-term obligations	1,400,000		1,400,000		1,600,000
Loss Contingencies
Litigation settlement expense						7,600,000
Payments for Legal Settlements							$ 6,500,000

Commitments and Contingencies - Schedule of Future Minimum Annual Commitments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015
Operating Leases
2015	$ 22,481
2016	45,034
2017	42,671
2018	40,961
2019	34,415
Thereafter	104,921
Total future lease commitments	290,483
Minimum Purchase Commitments
2015	19,384
2016	31,661
2017	21,529
2018	17,442
2019	11,147
Thereafter	16,778
Total future purchase commitments	$ 117,941

Income Taxes (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015 Selling, General and Administrative Expense
Loss Contingencies
Discrete tax benefit related to unfavorable ruling	$ 2.9
Litigation settlement expense			$ 7.6
Effective income tax rate	(13.00%)	27.00%
Effective income tax rate without discrete tax benefit	0.00

Pension and Post-Retirement Benefits (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Benefits
Defined Benefit Plan Disclosure
Contributions to plan by employer	$ 1.0	$ 1.9		$ 2.6
Expected contributions in current fiscal year			2.0
Post-retirement Benefits
Defined Benefit Plan Disclosure
Expected contributions in current fiscal year			$ 1.4

Pension and Post-Retirement Benefits - Summarizes Information about Pension and Post-Retirement Benefit Plans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 324	$ 270	$ 647	$ 539
Interest cost	1,203	1,142	2,406	2,285
Expected return on plan assets	(1,375)	(1,255)	(2,749)	(2,510)
Net amortization and deferral	666	238	1,333	476
Net pension benefit costs	818	395	1,637	790
Post-retirement Benefits
Defined Benefit Plan Disclosure
Service cost	44	45	88	90
Interest cost	277	257	554	514
Expected return on plan assets	(1)	(1)	(2)	(2)
Net amortization and deferral	96	0	192	0
Net pension benefit costs	$ 416	$ 301	$ 832	$ 602

Segment Reporting (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2015 Product Segment	Dec. 31, 2014
Segment Reporting Information
Number of reportable segments	2
Number of products in Industrial & Specialty segment (over 260)	260
Goodwill	$ 68,647	$ 68,647
Industrial & Specialty Products segment description	Over 260 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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information
Total Sales	$ 147,511	$ 205,801	$ 351,469	$ 385,896
Total segment contribution margin	32,788	74,675	100,438	129,490
Operating activities excluded from segment cost of goods sold	(2,477)	(1,291)	(4,822)	(2,781)
Selling, general and administrative	(6,575)	(19,267)	(33,536)	(34,712)
Depreciation, depletion and amortization	(13,695)	(10,341)	(26,938)	(19,930)
Interest expense	(6,249)	(4,013)	(13,085)	(7,821)
Other (expense)/income, net, including interest income	(181)	221	(170)	259
Income before income taxes	3,611	39,984	21,887	64,505
Operating Segments \| Oil & Gas Proppants
Segment Reporting Information
Total Sales	90,855	149,331	239,607	279,915
Total segment contribution margin	13,257	57,060	65,451	98,688
Operating Segments \| Industrial & Specialty Products
Segment Reporting Information
Total Sales	56,656	56,470	111,862	105,981
Total segment contribution margin	$ 19,531	$ 17,615	$ 34,987	$ 30,802

Subsequent Events (Details) (USD $)	6 Months Ended	0 Months Ended
Subsequent Events (Details) (USD $)	Jun. 30, 2015	Jul. 24, 2015 Subsequent Event	Jul. 06, 2015 Subsequent Event
Subsequent Event
Payable date	Apr. 03, 2015	Oct. 02, 2015	Jul. 06, 2015
Dividends, Common Stock, Cash	$ 13,393,000	$ 0.125	$ 0.125
Record date	Mar. 16, 2015	Sep. 15, 2015	Jun. 15, 2015
Declaration date	Feb. 12, 2015	Jul. 24, 2015	May 08, 2015

Subsequent Events	6 Months Ended
Subsequent Events	Jun. 30, 2015
Subsequent Events [Abstract]
Subsequent Events	On July 6, 2015, we paid a cash dividend of $0.125 per share to common stockholders of record on June 15, 2015, which had been declared by our Board of Directors on May 8, 2015. On July 24, 2015, our Board of Directors declared a quarterly cash dividend of $0.125 per share to common stockholders of record at the close of business on September 15, 2015, payable on October 2, 2015.

Obligations Under Guarantees (Detail) (Travelers Casualty and Surety Company, USD $) In Millions, unless otherwise specified	Jun. 30, 2015
Surety Bonds
Loss Contingencies
Surety bonds outstanding	$ 9.9
Reclamation Bonds
Loss Contingencies
Bonds related to reclamation requirements	$ 9.5

Asset Retirement Obligations (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation	$ 13,085	$ 11,283

Short-Term Investments (Detail) (USD $)	6 Months Ended
Short-Term Investments (Detail) (USD $)	Jun. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Impairment charges	$ 0