U.S. Silica (SLCA) 10-K 26 Feb 21 2020 FY Annual report Financial data

Cover

Cover - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 22, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-35416
Entity Registrant Name	U.S. Silica Holdings, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-3718801
Entity Address, Address Line One	24275 Katy Freeway, Suite 600
Entity Address, City or Town	Katy
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77494
City Area Code	281
Local Phone Number	258-2170
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	SLCA
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 250,637,123
Entity Common Stock, Shares Outstanding		74,296,160
Documents Incorporated by Reference	Certain sections of the Proxy Statement for the 2021 Annual Meeting of Shareholders for U.S. Silica Holdings, Inc. (the “2021 Proxy Statement”) are incorporated by reference in Part III of this Annual Report on Form 10-K where indicated.
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001524741
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 150,920	$ 185,740
Accounts receivable, net	206,934	182,238
Inventories, net	104,684	124,432
Prepaid expenses and other current assets	23,147	16,155
Income tax deposits	628	475
Total current assets	486,313	509,040
Property, plant and mine development, net	1,368,092	1,517,587
Operating lease right-of-use assets	37,469	53,098
Goodwill	185,649	273,524
Intangible assets, net	159,582	183,815
Other assets	9,842	16,170
Total assets	2,246,947	2,553,234
Current Liabilities:
Accounts payable and accrued expenses	121,920	248,237
Current portion of operating lease liabilities	17,388	53,587
Current portion of long-term debt	42,042	18,463
Current portion of deferred revenue	13,545	15,111
Total current liabilities	194,895	335,398
Long-term debt, net	1,197,660	1,213,985
Deferred revenue	20,147	35,523
Liability for pension and other post-retirement benefits	48,169	58,453
Deferred income taxes, net	49,386	38,585
Operating lease liabilities	76,361	117,964
Other long-term obligations	33,538	36,746
Total liabilities	1,620,156	1,836,654
Commitments and Contingencies (Note P)
Stockholders’ Equity:
Preferred stock, $0.01 par value, 10,000,000 shares authorized; zero issued and outstanding at December 31, 2020 and 2019	0	0
Common stock, $0.01 par value, 500,000,000 shares authorized; 83,143,176 issued and 73,986,566 outstanding at December 31, 2020; 82,601,926 issued and 73,601,950 outstanding at December 31, 2019	827	823
Additional paid-in capital	1,200,023	1,185,116
Retained deficit	(395,496)	(279,956)
Treasury stock, at cost, 9,156,610 and 8,999,976 shares at December 31, 2020 and 2019, respectively	(181,615)	(180,912)
Accumulated other comprehensive loss	(8,479)	(19,854)
Total U.S. Silica Holdings, Inc. stockholders’ equity	615,260	705,217
Non-controlling interest	11,531	11,363
Total stockholders' equity	626,791	716,580
Total liabilities and stockholders’ equity	$ 2,246,947	$ 2,553,234

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock authorized (shares)	10,000,000	10,000,000
Preferred stock issued (shares)	0	0
Preferred stock outstanding (shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock authorized (shares)	500,000,000	500,000,000
Common stock issued (shares)	83,143,176	82,601,926
Common stock outstanding (shares)	73,986,566	73,601,950
Treasury stock, at cost (shares)	9,156,610	8,999,976

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Sales:
Total sales									$ 845,885	$ 1,474,477	$ 1,577,298
Cost of sales (excluding depreciation, depletion and amortization):
Total cost of sales (excluding depreciation, depletion and amortization)									575,070	1,133,293	1,163,129
Operating expenses:
Selling, general and administrative	$ 27,777	$ 27,216	$ 39,126	$ 30,052	$ 37,325	$ 40,208	$ 38,659	$ 34,656	124,171	150,848	146,971
Depreciation, depletion and amortization	39,964	40,069	37,086	38,449	42,819	47,126	44,899	44,600	155,568	179,444	148,832
Goodwill and other asset impairments	2,644	222	3,956	103,866	363,717	130	0	0	110,688	363,847	281,899
Total operating expenses	70,385	67,507	80,168	172,367	443,861	87,464	83,558	79,256	390,427	694,139	577,702
Operating loss	15,474	1,373	(32,374)	(104,085)	(362,764)	(9,283)	17,136	1,956	(119,612)	(352,955)	(163,533)
Other (expense) income:
Interest expense	(16,155)	(19,274)	(22,179)	(22,277)	(22,996)	(24,733)	(23,765)	(23,978)	(79,885)	(95,472)	(70,564)
Other income (expense), net, including interest income	8,758	(409)	(1,670)	17,671	443	3,280	15,074	722	24,350	19,519	4,144
Total other expense	(7,397)	(19,683)	(23,849)	(4,606)	(22,553)	(21,453)	(8,691)	(23,256)	(55,535)	(75,953)	(66,420)
Loss before income taxes	8,077	(18,310)	(56,223)	(108,691)	(385,317)	(30,736)	8,445	(21,300)	(175,147)	(428,908)	(229,953)
Income tax benefit	(3,760)	4,094	23,605	36,086	91,892	7,671	(2,384)	1,972	60,025	99,151	29,132
Net loss	4,317	(14,216)	(32,618)	(72,605)	(293,425)	(23,065)	6,061	(19,328)	(115,122)	(329,757)	(200,821)
Less: Net loss attributable to non-controlling interest	(250)	(254)	(264)	(260)	(554)	(28)	(89)	(4)	(1,028)	(675)	(13)
Net loss attributable to U.S. Silica Holdings, Inc.	$ 4,567	$ (13,962)	$ (32,354)	$ (72,345)	$ (292,871)	$ (23,037)	$ 6,150	$ (19,324)	$ (114,094)	$ (329,082)	$ (200,808)
Loss per share attributable to U.S. Silica Holdings, Inc.:
Basic (in dollars per share)	$ 0.06	$ (0.19)	$ (0.44)	$ (0.98)	$ (4)	$ (0.31)	$ 0.08	$ (0.26)	$ (1.55)	$ (4.49)	$ (2.63)
Diluted (in dollars per share)	$ 0.06	$ (0.19)	$ (0.44)	$ (0.98)	$ (4)	$ (0.31)	$ 0.08	$ (0.26)	$ (1.55)	$ (4.49)	$ (2.63)
Weighted average shares outstanding:
Basic (shares)	73,728	73,688	73,620	73,467	73,343	73,328	73,301	73,040	73,634	73,253	76,453
Diluted (shares)									73,634	73,253	76,453
Dividends declared per share (in dollars per share)	$ 0	$ 0	$ 0	$ 0.02	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.02	$ 0.25	$ 0.25
Product
Sales:
Total sales	$ 190,189	$ 159,637	$ 160,200	$ 222,161	$ 280,594	$ 287,977	$ 303,041	$ 296,860	$ 732,187	$ 1,168,472	$ 1,282,799
Cost of sales (excluding depreciation, depletion and amortization):
Total cost of sales (excluding depreciation, depletion and amortization)	113,609	93,747	114,130	165,496	212,905	226,797	225,473	234,916	486,982	900,091	955,469
Service
Sales:
Total sales	37,088	16,835	12,337	47,438	58,465	73,837	91,813	81,890	113,698	306,005	294,499
Cost of sales (excluding depreciation, depletion and amortization):
Total cost of sales (excluding depreciation, depletion and amortization)	$ 27,809	$ 13,845	$ 10,613	$ 35,821	$ 45,057	$ 56,836	$ 68,687	$ 62,622	$ 88,088	$ 233,202	$ 207,660

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ 4,317	$ (14,216)	$ (32,618)	$ (72,605)	$ (293,425)	$ (23,065)	$ 6,061	$ (19,328)	$ (115,122)	$ (329,757)	$ (200,821)
Other comprehensive (loss) income:
Unrealized gain (loss) on derivatives (net of tax of $973, $(456), and $(470) for 2020, 2019, and 2018, respectively)									3,053	(1,432)	(1,545)
Foreign currency translation adjustment (net of tax of $444, $(60), and $(196) for 2020, 2019 and 2018, respectively)									1,391	(188)	(614)
Pension and other post-retirement benefits liability adjustments (net of tax of $2,207, $(1,024), and $339 for 2020, 2019 and 2018, respectively)									6,931	(3,214)	1,065
Comprehensive loss									(103,747)	(334,591)	(201,915)
Less: Comprehensive loss attributable to non-controlling interest									(1,028)	(675)	(13)
Comprehensive loss attributable to U.S. Silica Holdings, Inc.									$ (102,719)	$ (333,916)	$ (201,902)

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Tax expense (benefit) on unrealized gain (loss) on derivatives	$ 973	$ (456)	$ (470)
Tax expense (benefit) on foreign currency translation adjustment	444	(60)	(196)
Tax (expense) benefit on pension and other post-retirement benefits liability adjustment	$ 2,207	$ (1,024)	$ 339

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Total U.S. Silica Holdings Inc., Stockholders’ Equity	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings (Deficit)	Accumulated Other Comprehensive Loss	Non-controlling Interest
Beginning Balance at Dec. 31, 2017	$ 1,396,506	$ 1,396,506	$ 812	$ (25,456)	$ 1,147,084	$ 287,992	$ (13,926)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(200,821)	(200,808)				(200,808)		(13)
Unrealized gain (loss) on derivatives	(1,545)	(1,545)					(1,545)
Foreign currency translation adjustment	(614)	(614)					(614)
Pension and post-retirement liability	1,065	1,065					1,065
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)	(19,330)	(19,330)				(19,330)
Contributions from non-controlling interest	7,497							7,497
Common stock-based compensation plans activity:
Equity-based compensation	22,337	22,337			22,337
Proceeds from options exercised	61	61		93	(32)
Shares withheld for tax payments related to vested restricted stock and stock units	(4,383)	(4,383)	6	(4,383)	(6)
Repurchase of common stock	(148,469)	(148,469)		(148,469)
Ending Balance at Dec. 31, 2018	1,052,304	1,044,820	818	(178,215)	1,169,383	67,854	(15,020)	7,484
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(329,757)	(329,082)				(329,082)		(675)
Unrealized gain (loss) on derivatives	(1,432)	(1,432)					(1,432)
Foreign currency translation adjustment	(188)	(188)					(188)
Pension and post-retirement liability	(3,214)	(3,214)					(3,214)
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)	(18,728)	(18,728)				(18,728)
Contributions from non-controlling interest	4,554							4,554
Common stock-based compensation plans activity:
Equity-based compensation	15,906	15,906			15,906
Proceeds from options exercised	128	128		296	(168)
Shares withheld for tax payments related to vested restricted stock and stock units	(2,993)	(2,993)	5	(2,993)	(5)
Ending Balance at Dec. 31, 2019	716,580	705,217	823	(180,912)	1,185,116	(279,956)	(19,854)	11,363
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(115,122)	(114,094)				(114,094)		(1,028)
Unrealized gain (loss) on derivatives	3,053	3,053					3,053
Foreign currency translation adjustment	1,391	1,391					1,391
Pension and post-retirement liability	6,931	6,931					6,931
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)	(1,446)	(1,446)				(1,446)
Contributions from non-controlling interest	1,196							1,196
Common stock-based compensation plans activity:
Equity-based compensation	14,911	14,911			14,911
Shares withheld for tax payments related to vested restricted stock and stock units	(703)	(703)	4	(703)	(4)
Ending Balance at Dec. 31, 2020	$ 626,791	$ 615,260	$ 827	$ (181,615)	$ 1,200,023	$ (395,496)	$ (8,479)	$ 11,531

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Stockholders' Equity [Abstract]
Cash dividend declared (in dollars per share)	$ 0	$ 0	$ 0	$ 0.02	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.02	$ 0.25	$ 0.25

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net loss	$ (115,122,000)	$ (329,757,000)	$ (200,821,000)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation, depletion and amortization	155,568,000	179,444,000	148,832,000
Goodwill and other asset impairments	110,688,000	363,847,000	281,899,000
Debt issuance amortization	5,131,000	5,597,000	4,044,000
Original issue discount amortization	1,036,000	1,053,000	832,000
Gain on valuation change of royalty note payable	(8,263,000)	(16,854,000)	0
Inventory step-up adjustments	0	22,373,000	20,107,000
Deferred income taxes	(61,805,000)	(101,682,000)	(31,070,000)
Deferred revenue	(23,569,000)	(74,910,000)	(36,720,000)
(Gain) loss on disposal of property, plant and equipment	(2,597,000)	1,573,000	(5,170,000)
Equity-based compensation	14,911,000	15,906,000	22,337,000
Provision for credit losses, net of recoveries	1,510,000	3,466,000	315,000
Gain on remeasurement of leases	(24,056,000)	0	0
Other	23,146,000	(12,042,000)	(13,536,000)
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	48,441,000	33,837,000	56,815,000
Inventories	15,245,000	11,182,000	(7,022,000)
Prepaid expenses and other current assets	(6,151,000)	8,547,000	(2,678,000)
Income taxes	(153,000)	1,725,000	(3,764,000)
Accounts payable and accrued expenses	(86,734,000)	21,024,000	26,907,000
Short-term and long-term obligations-vendor incentives	0	4,021,000	52,806,000
Liability for pension and other post-retirement benefits	(11,941,000)	2,734,000	4,608,000
Other noncurrent assets and liabilities	(45,819,000)	2,962,000	(8,015,000)
Net cash (used in) provided by operating activities	(10,534,000)	144,046,000	310,706,000
Investing activities:
Capital expenditures	(34,461,000)	(118,357,000)	(339,815,000)
Capitalized intellectual property costs	(456,000)	(3,932,000)	(10,046,000)
Acquisition of businesses, net of cash acquired	0	0	(743,249,000)
Proceeds from sale of property, plant and equipment	7,353,000	1,896,000	26,231,000
Net cash used in investing activities	(27,564,000)	(120,393,000)	(1,066,879,000)
Financing activities:
Dividends paid	(6,185,000)	(18,592,000)	(19,912,000)
Repurchase of common stock	0	0	(148,469,000)
Proceeds from options exercised	0	128,000	61,000
Tax payments related to shares withheld for vested restricted stock and stock units	(703,000)	(2,993,000)	(4,383,000)
Proceeds from long-term debt	0	0	1,280,000,000
Proceeds from draw down on the Revolver	25,000,000	0	0
Payments on long-term debt	(15,985,000)	(23,449,000)	(501,425,000)
Financing fees paid	0	0	(38,701,000)
Contributions from non-controlling interest	1,196,000	4,554,000	7,497,000
Principal payments on finance lease obligations	(45,000)	(59,000)	(564,000)
Net cash provided by (used in) financing activities	3,278,000	(40,411,000)	574,104,000
Net decrease in cash and cash equivalents	(34,820,000)	(16,758,000)	(182,069,000)
Cash and cash equivalents, beginning of period	185,740,000	202,498,000	384,567,000
Cash and cash equivalents, end of period	150,920,000	185,740,000	202,498,000
Cash paid (received) during the period for:
Interest	73,695,000	87,286,000	66,769,000
Taxes, net of refunds	(39,908,000)	(14,741,000)	5,373,000
Related party purchases	0	0	2,958,000
Non-cash Items:
Net assets assumed in business acquisition	8,241,000	0	0
Accrued capital expenditures	26,136,000	27,646,000	36,008,000
Capital lease assumed by third-party	0	0	119,000
Asset retirement obligation assumed by third-party	$ 0	$ 0	$ 2,116,000

Organization

Organization	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION	NOTE A—ORGANIZATION U.S. Silica Holdings, Inc. (“Holdings,” and together with its subsidiaries “we,” “us” or the “Company”) is a performance materials company and one of the largest producers of commercial silica used in the oil and gas industry and in a wide range of industrial applications. In addition, through our subsidiary EP Minerals, LLC ("EPM") we are an industry leader in the production of industrial minerals, including diatomaceous earth, clay (calcium bentonite and calcium montmorillonite) and perlite. During our 121-year history, we have developed core competencies in mining, processing, logistics and materials science that enable us to produce and cost-effectively deliver products to customers across our end markets. Our operations are organized into two reportable segments based on end markets served: (1) Oil & Gas Proppants and (2) Industrial & Specialty Products. See Note V - Segment Reporting for more information on our reportable segments.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NOTE B—SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation and Consolidation The accompanying Consolidated Financial Statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). In the opinion of management, all adjustments necessary for a fair presentation of the Consolidated Financial Statements have been included. Such adjustments are of a normal, recurring nature. Throughout this report we refer to (i) our Consolidated Balance Sheets as our “Balance Sheets,” (ii) our Consolidated Statements of Operations as our “Income Statements,” and (iii) our Consolidated Statements of Cash Flows as our “Cash Flows.” Consolidation The Consolidated Financial Statements include the accounts of Holdings and its direct and indirect wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. We follow FASB Accounting Standards Codification (“ASC”) guidance for identification and reporting of entities over which control is achieved through means other than voting rights. The guidance defines such entities as Variable Interest Entities (“VIEs”). We consolidate VIEs when we have variable interests and are the primary beneficiary. We continually evaluate our involvement with VIEs to determine when these criteria are met. During the third quarter of 2018 we finalized a shareholders' agreement with unrelated parties to form a limited liability company with the purpose of constructing and operating a water pipeline to transport and sell water. In connection with the shareholders’ agreement, we acquired a 50% equity ownership for $3.2 million, with a maximum initial capital contribution of $7.0 million, and a water rights intangible asset for $0.7 million. Based on our evaluation, we determined that this limited liability company is a VIE of which we are the primary beneficiary and therefore we are required to consolidate it. As of December 31, 2020, the VIE had total assets of $17.3 million and total liabilities of $0.1 million. We made capital contributions in the amounts of $0.2 million and $0.4 million during the years ended December 31, 2020 and December 31, 2019, respectively. Reclassifications Certain reclassifications of prior period presentations have been made to conform to the current period presentation. Use of Estimates and Assumptions The preparation of Consolidated Financial Statements in conformity with GAAP requires management 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 Consolidated Financial Statements and the reported amounts of revenues and expenses during the reporting period. The areas requiring the use of management estimates and assumptions relate to the purchase price allocation for businesses acquired; 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 provision for credit losses; estimates of fair value for certain reporting units and asset impairments (including impairments of goodwill, intangible assets 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; contingent considerations; 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. Cash and Cash Equivalents Cash and cash equivalents consist of all highly liquid investments with a maturity of three months or less when purchased. Because of the short maturity of these investments, the carrying amounts approximate their fair value. Cash and cash equivalents are invested primarily in money market securities held by financial institutions with high credit ratings. Accounts at each institution are insured by the Federal Deposit Insurance Corporation. Cash balances at times may exceed federally-insured limits. We have not experienced any losses in such accounts and believe we are not exposed to any significant credit risk on cash. Accounts Receivable The majority of our accounts receivable are due from companies in the oil and natural gas drilling, building and construction products, filler and extenders, filtration, glass, absorbents, sports and recreation, foundry and other major industries. Credit is extended based on evaluation of a customer’s financial condition and, generally, collateral is not required. Accounts receivable are stated at amounts due from customers net of provision for credit losses. Accounts outstanding longer than the payment terms are considered past due. We determine our allowance by considering a number of factors, including the length of time trade accounts receivable are past due, our previous loss history, the customer’s current ability to pay its obligation to us and the condition of the general economy and the industry as a whole. Ongoing credit evaluations are performed. We write-off accounts receivable when they are deemed uncollectible, and payments subsequently received on such receivables are credited to the provision for credit losses. See Note F - Accounts Receivable and Note T - Revenue. Inventories Inventories include raw stockpiles, in-process product and finished product available for shipment, as well as spare parts and supplies for routine facility maintenance. We value inventory at the lower of cost and net realizable value. Cost is determined using the first-in, first-out and average cost methods. Our inventoriable costs include production costs and transportation and additional service costs as applicable. See Note G - Inventories. Property, Plant and Mine Development Plant and equipment Plant and equipment is recorded at cost and depreciated over their estimated useful lives. Interest incurred during construction of facilities is capitalized and depreciated over the life of the asset. Costs for normal repairs and maintenance that do not extend economic life or improve service potential are expensed as incurred. Costs of improvements that extend economic life or improve service potential are capitalized and depreciated over the estimated remaining useful life. Depreciation is recorded using the straight-line method over the assets’ estimated useful lives as follows: buildings (15 years); land improvements (10 years); machinery and equipment, including computer equipment and software (3-10 years); furniture and fixtures (8 years). Leasehold improvements are depreciated over the shorter of the asset life or lease term. Construction-in-progress is primarily comprised of machinery and equipment which have not yet been placed in service. Mining property and development Mining property and development includes mineral deposits and mine exploration and development. Mineral deposits are initially recognized at cost, which approximates the estimated fair value on the date of purchase. Mine exploration and development costs include engineering and mineral studies, drilling and other related costs to delineate an ore body, and the removal of overburden to initially expose an ore body for production. Costs incurred before mineralization are classified as proven and probable reserves are expensed and classified as exploration or advanced projects, research and development expense. Capitalization of mine development project costs, which meet the definition of an asset, begins once mineralization is classified as proven and probable reserves. The cost of removing overburden and waste materials to access the ore body at an open pit mine prior to the production phase are referred to as “pre-stripping costs.” Pre-stripping costs are capitalized during the development of an open pit mine. The production phase of an open pit mine commences when saleable minerals, beyond a de minimis amount, are produced. Stripping costs incurred during the production phase of a mine are variable production costs that are included as a component of inventory to be recognized in costs applicable to sales in the same period as the revenue from the sale of inventory. Depletion and amortization of mineral deposits and mine development costs are recorded as the minerals are extracted, based on units of production and engineering estimates of mineable reserves. The impact of revisions to reserve estimates is recognized on a prospective basis. See Note H - Property, Plant and Mine Development. Mine reclamation costs and asset retirement obligations We recognize the fair value of any liability for conditional asset retirement obligations, if sufficient information exists to reasonably estimate the fair value of the liability. These obligations include environmental remediation liabilities when incurred, which is generally upon acquisition, construction or development and/or through the normal operation of the asset. These obligations also generally include the estimated net future costs of dismantling, restoring and reclaiming operating mines and related mine sites in accordance with federal, state, local regulatory and land lease agreement requirements. The liability is accreted over time through periodic charges to earnings. In addition, the asset retirement cost is capitalized as part of the asset’s carrying value and amortized over the life of the related asset. Reclamation costs are periodically adjusted to reflect changes in the estimated present value resulting from the passage of time and revisions to the estimates of either the timing or amount of the reclamation and abandonment costs. The reclamation obligation is based on when spending for an existing environmental disturbance will occur. If the asset retirement obligation is settled for other than the carrying amount of the liability, a gain or loss is recognized on settlement. We review, on an annual basis, unless otherwise deemed necessary, the reclamation obligation at each mine site in accordance with ASC guidance for accounting for reclamation obligations. See Note L - Asset Retirement Obligations. Impairment or Disposal of Property, Plant and Mine Development We periodically evaluate whether current events or circumstances indicate that the carrying value of our property, plant and equipment assets may not be recoverable. If circumstances indicate that the carrying value may not be recoverable, we estimate future undiscounted net cash flows using estimates of proven and probable sand reserves, estimated future sales prices (considering historical and current prices, price trends and related factors) and operating costs and anticipated capital expenditures. If the undiscounted cash flows are less than the carrying value of the assets we recognize an impairment loss equal to the amount by which the carrying value exceeds the fair value of the assets. The recoverability of the carrying value of our mineral properties is dependent upon the successful development, start-up and commercial production of our mineral deposit and the related processing facilities. Our evaluation of mineral properties for potential impairment primarily includes assessing the existence or availability of required permits and evaluating changes in our mineral reserves, or the underlying estimates and assumptions, including estimated production costs. Assessing the economic feasibility requires certain estimates including the prices of products to be produced and processing recovery rates, as well as operating and capital costs. Gains on the sale of property, plant and mine development are included in income when the assets are disposed of provided there is more than reasonable certainty of the collectability of the sales price and any future activities required to be performed by us relating to the disposal of the assets are complete or insignificant. Upon retirement or disposal of assets, all costs and related accumulated depreciation or amortization are written-off. Goodwill and Other Intangible Assets and Related Impairment Our intangible assets consist of goodwill, which is not being amortized, indefinite-lived intangibles, which consist of certain trade names that are not subject to amortization, intellectual property and customer relationships. Intellectual property mainly consists of patents and technology, and it is amortized on a straight-line basis over an average useful life of 15 years. Customer relationships are amortized on a straight-line basis over their useful life of 13 - 20 years. Intangible assets that are amortized are reviewed for impairment annually, or more frequently when indicators of impairment exist. Goodwill represents the excess of the purchase price of business combinations over the fair value of net assets acquired. Goodwill and trade names are reviewed for impairment annually as of October 31, or more frequently when indicators of impairment exist. An impairment exists if the fair value of a reporting unit to which goodwill has been allocated, or the fair value of indefinite-lived intangible assets, is less than their respective carrying values. Prior to conducting a formal impairment test we have an option to assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that is more likely than not (more than 50%) that the fair value of a reporting unit is less than its carrying amount. Such qualitative factors may include the following: macroeconomic conditions; industry and market considerations; cost factors; overall financial performance; and other relevant entity-specific events. If the qualitative assessment determines that an impairment is more likely than not, or if we choose to bypass the qualitative assessment, we perform a quantitative assessment by comparing the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. See Note I - Goodwill and Intangible Assets. Leases We lease railroad cars, office space, mining property, mining/processing equipment and transportation and other equipment. Operating leases are included in operating lease right-of-use (“ROU”) assets, current portion of operating lease liabilities, and operating lease liabilities in our consolidated balance sheets. Finance leases are included in property, plant and mine development, current portion of long-term debt, and long-term debt in our consolidated balance sheets. Leases with an initial term of 12 months or less are not recorded on the balance sheet. ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and liabilities are recognized at the commencement date of the lease based on the present value of lease payments over the lease term. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. The ROU assets also include any lease payments made at or before the commencement date of the lease and excludes lease incentives. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term. We have lease agreements with lease and non-lease components, the latter of which are generally accounted for separately. See Note R - Leases. We periodically evaluate whether current events or circumstances indicate that the carrying value of our ROU assets exceeds fair value. If circumstances indicate an impairment exists, we estimate fair value primarily utilizing internally developed cash flow models and quoted market prices, discounted at an appropriate weighted average cost of capital. If the undiscounted cash flows are less than the carrying value of the assets, we recognize an impairment loss equal to the amount by which the carrying value exceeds the fair value of the assets. Revenue Recognition Products We derive our product sales by mining and processing minerals that our customers purchase for various uses. Our product sales are primarily a function of the price per ton and the number of tons sold. We primarily sell our products through individual purchase orders executed under short-term price agreements or at prevailing market rates. The amount invoiced reflects product, transportation and additional handling services as applicable, such as storage, transloading the product from railcars to trucks and last mile logistics to the customer site. We invoice most of our product customers on a per shipment basis, although for some larger customers, we consolidate invoices weekly or monthly. Standard collection terms are net 30 days, although extended terms are offered in competitive situations. We recognize revenue for products and materials at a point in time following the transfer of control of such items to the customer, which typically occurs upon shipment or delivery depending on the terms of the underlying contracts. We account for shipping and handling activities related to product and material sales contracts with customers as costs to fulfill our promise to transfer the associated products pursuant to the accounting policy election allowed under ASC 606-10-25-18b. Accordingly, we record amounts billed for shipping and handling costs as a component of net sales and accrue and classify related costs as a component of cost of sales at the time revenue is recognized. For a limited number of customers, we sell under long-term, minimum purchase supply agreements. These agreements define, among other commitments, the volume of product that our customers must purchase, the volume of product that we must provide and the price that we will charge and that our customers will pay for each product. Prices under these agreements are generally fixed and subject to certain contractual adjustments. Sometimes these agreements may undergo negotiations regarding pricing and volume requirements, which may often occur in volatile market conditions. While these negotiations continue, we may deliver sand at prices or at volumes below the requirements in our existing supply agreements. An executed order specifying the type and quantity of product to be delivered, in combination with the noted agreements, comprise our contracts in these arrangements. Service We derive our service revenues primarily through the provision of transportation, equipment rental, and contract labor services to companies in the oil and gas industry. Transportation services typically consist of transporting customer proppant from storage facilities to proximal well-sites and are contracted through work orders executed under established pricing agreements. The amount invoiced reflects the transportation services rendered. Equipment rental services provide customers with use of either dedicated or nonspecific wellhead proppant delivery equipment solutions for contractual periods defined either through formal lease agreements or executed work orders under established pricing agreements. The amounts invoiced reflect the length of time the equipment set was utilized in the billing period. Contract labor services provide customers with proppant delivery equipment operators through work orders executed under established pricing agreements. The amounts invoiced reflect the amount of time our labor services were utilized in the billing period. We typically invoice our customers on a weekly or monthly basis; however, some customers receive invoices upon well-site operation completion. Standard collection terms are net 30 days, although extended terms are offered in competitive situations. We typically recognize revenue for specific, dedicated equipment set rental arrangements under ASC 842, Leases. For the remaining components of service revenue, we have applied the practical expedient allowed under ASC 606-10-55-18 to recognize transportation revenues in proportion to the amount we have the right to invoice. Contracts with Multiple Performance Obligations From time to time, we may enter into contracts that contain multiple performance obligations, such as work orders containing a combination of product, transportation, equipment rentals, and contract labor services. For these arrangements, we allocate the transaction price to each performance obligation identified in the contract based on relative standalone selling prices, or estimates of such prices, and recognize the related revenue as control of each individual product or service is transferred to the customer, in satisfaction of the corresponding performance obligations. We typically invoice our customers on a weekly or monthly basis; however, some customers receive invoices upon well-site operation completion. Standard collection terms are net 30 days, although extended terms are offered in competitive situations. Taxes Collected from Customers and Remitted to Governmental Authorities. We exclude from our measurement of transaction prices all taxes assessed by governmental authorities that are both (i) imposed on and concurrent with a specific revenue-producing transaction and (ii) collected from customers. Accordingly, such tax amounts are not included as a component of net sales or cost of sales. See Note T - Revenue. Deferred Revenues For a limited number of customers, we enter into supply agreements which give customers the right to make advanced payments toward the purchase of certain products at specified volumes over an average initial period of one Unbilled Receivables Revenues recognized in advance of invoice issuance create assets referred to as “unbilled receivables.” Any portion of our unbilled receivables for which our right to consideration is conditional on a factor other than the passage of time is considered a contract asset. These assets are presented on a combined basis with accounts receivable and are converted to accounts receivable once billed. Debt Issuance Costs The Company defers costs directly associated with acquiring third-party financing, primarily loan origination costs and related professional expenses. Debt issuance costs are deferred and amortized using the effective interest rate method over the term of our senior secured Term Loan facility and the straight-line method for our Revolver facility. Debt issuance costs related to long-term debt are reflected as a direct deduction from the carrying amount of the debt. Amortization included in interest expense was $5.1 million for the year ended December 31, 2020, and $5.6 million and $4.0 million for the years ended December 31, 2019 and 2018. See Note K - Debt. Employee Benefit Plans We provide a range of benefits to our employees and retired employees, including pensions and post-retirement healthcare and life insurance benefits. We record annual amounts relating to these plans based on calculations specified by generally accepted accounting principles, which include various actuarial assumptions, including discount rates, assumed rates of returns, compensation increases, turnover rates, mortality tables, and healthcare cost trend rates. We review the actuarial assumptions on an annual basis and make modifications to the assumptions based on current rates and trends when it is deemed appropriate to do so. As required by U.S. generally accepted accounting principles, the effect of the modifications is generally recorded or amortized over future periods. We believe that the assumptions utilized in recording our obligations under the plans are reasonable based on advice from our actuaries and information as to assumptions used by other employers. See Note Q - Pension and Post-Retirement Benefits. Environmental Costs Environmental costs, other than qualifying capital expenditures, are accrued at the time the exposure becomes known and costs can be reasonably estimated. Costs are accrued based upon management’s estimates of all direct costs, after taking into account expected reimbursement by third parties (primarily the sellers of acquired businesses) and are reviewed by outside consultants. Environmental costs are charged to expense unless a settlement with an indemnifying party has been reached. Self-Insurance We are self-insured for various levels of employee health insurance coverage, workers’ compensation and third-party product liability claims alleging occupational disease. We purchase insurance coverage for claim amounts which exceed our self-insured retentions. Depending on the type of insurance, these self-insured retentions range from $0.1 million to $0.5 million per occurrence. Our insurance reserves are accrued based on estimates of the ultimate cost of claims expected to occur during the covered period. These estimates are prepared with the assistance of outside actuaries and consultants. Our actuaries periodically review the volume and amount of claims activity, and based upon their findings, we adjust our insurance reserves accordingly. The ultimate cost of claims for a covered period may differ from our original estimates. The current portion of our self-insurance reserves is included in accrued liabilities and the non-current portion is included in other long-term obligations in our Balance Sheets. As of December 31, 2020 and 2019, our self-insurance reserves totaled $4.8 million and $6.6 million, respectively, of which $1.8 million and $4.1 million, respectively, were classified as current. Research and Development Costs We may incur immaterial internal research and development (“R&D”) expenditures, and research and development conducted for others, all of which are expensed as incurred, and included in selling, general and administrative expense. R&D costs may include, but are not limited to, research and administrative salaries, contractor fees, building costs, utilities, administrative expenses, and allocations of corporate costs. Advertising Costs We recognize advertising expense when incurred as selling, general and administrative expense. Advertising costs have not been a significant component of expense for the years ended December 31, 2020, 2019, or 2018. Equity-based Compensation We grant stock options, restricted stock, restricted stock units and performance share units to certain of our employees and directors under the Amended and Restated U.S. Silica Holdings, Inc. 2011 Incentive Compensation Plan. We recognize the cost of employee services rendered in exchange for awards of equity instruments. Vesting of restricted stock and restricted stock units is based on the individual continuing to render service over a pre-defined vesting schedule, generally three years. Cash dividend equivalents are accrued and paid to the holders of time-based restricted stock units and restricted stock. The fair value of the restricted stock awards is equal to the market price of our stock at date of grant. The restricted award-related compensation expense is recognized on a straight-line basis over the vesting period. We grant performance share units to certain employees in which the number of shares of common stock ultimately received is determined based on achievement of certain performance thresholds over a specified performance period (generally three years) in accordance with the stock award agreement. Cash dividend equivalents are not accrued or paid on performance share units. We recognize expense based on the estimated vesting of our performance share units granted and the grant date market price. The estimated vesting of the performance share units is principally based on the probability of achieving certain financial performance levels during the vesting periods. In the period it becomes probable that the minimum performance criteria specified in the award agreement will be achieved, we recognize expense for the proportionate share of the total fair value of the award related to the vesting period that has already lapsed. The remaining fair value of the award is expensed on a straight-line basis over the remaining vesting period. We grant certain employees performance share units, the vesting of which is based on the Company’s total shareholder return (“TSR”) ranking among a peer group over a three-year period. The number of units that will vest will depend on the percentage ranking of the Company's TSR compared to the TSRs for each of the companies in the peer group over the performance period. For these awards subject to market conditions, a binomial-lattice model (i.e., Monte Carlo simulation model) is used to fair value these awards at grant date. The related compensation expense is recognized, on a straight-line basis, over the vesting period. We grant stock options to certain employees and directors. Stock options vest on a vesting schedule and the related compensation expense is recognized over the vesting period, usually over three The fair value of stock options granted is based on the exercise price of the option and certain assumptions, which are evaluated and revised, as necessary, to reflect market conditions and experience. We account for forfeitures as they occur. Our expected term is the period of time over which the options are expected to remain outstanding. An increase in the expected term will increase compensation expense. The computation of the expected term is based on the simplified method, under which the expected term is presumed to be the mid-point between the average vesting date and the end of the contractual term. The assumptions for expected volatility are based on historical experience for the same periods as our expected lives. Risk-free interest rates are set using grant-date U.S. Treasury yield curves for the same periods as our expected lives. The expected dividend yield is based on our future dividend expectations for the same periods as our expected lives. See Note O - Equity-based Compensation. Income Taxes Deferred taxes are provided on the liability method whereby deferred tax assets are recognized for deductible temporary differences and operating loss and tax credit carry forwards and deferred tax liabilities are recognized for taxable temporary differences. This approach requires recognition of deferred tax liabilities and assets for the expected future tax consequences of events that have been included in the financial statements or tax returns. Under this method, deferred tax liabilities and assets are determined based upon the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the expenses are expected to reverse. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. We recognize a tax benefit associated with an uncertain tax position when, in management’s judgment, it is more likely than not that the position will be sustained upon examination by a taxing authority. For a tax position that meets the more-likely-than-not recognition threshold, we initially and subsequently measure the tax benefit as the largest amount that we judge to have a greater than 50% likelihood of being realized upon ultimate settlement with a taxing authority. The liability associated with unrecognized tax benefits is adjusted periodically due to changing circumstances, such as the progress of tax audits, case law developments and new or emerging legislation. Such adjustments are recognized entirely in the period in which they are identified. The effective tax rate includes the net impact of changes in the liability for unrecognized tax benefits and subsequent adjustments as considered appropriate by management. Generally, the largest permanent item in computing both our effective tax rate and taxable income is the deduction allowed for statutory depletion. The deduction for statutory depletion does not necessarily change p

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
EARNINGS PER SHARE	NOTE C—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 earnings 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. The following table shows the computation of basic and diluted earnings per share for the years ended December 31, 2020, 2019 and 2018: In thousands, except per share amounts Year ended December 31, 2020 2019 2018 Numerator: Net loss attributable to U.S. Silica Holdings, Inc. $ (114,094) $ (329,082) $ (200,808) Denominator: Weighted average shares outstanding 73,634 73,253 76,453 Diluted effect of stock awards — — — Weighted average shares outstanding assuming dilution 73,634 73,253 76,453 Loss per share attributable to U.S. Silica Holdings, Inc.: Basic loss per share $ (1.55) $ (4.49) $ (2.63) Diluted loss per share $ (1.55) $ (4.49) $ (2.63) Potentially dilutive shares were excluded from the calculation of diluted weighted average shares outstanding and diluted earnings per share because we were in a loss position. Certain stock options, restricted stock awards and performance share units were excluded from the computation of diluted earnings per share because their effect would have been anti-dilutive. Such potentially dilutive shares and stock awards (in thousands) excluded from the calculation of diluted earnings (loss) per common share were as follows: Year ended December 31, 2020 2019 2018 Potentially dilutive shares excluded 238 68 443 Stock options excluded 826 711 574 Restricted stock and performance share units awards excluded 3,435 1,298 155

Capital Structure and Accumulat

Capital Structure and Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
CAPITAL STRUCTURE AND ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	NOTE D—CAPITAL STRUCTURE AND ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) 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 83,143,176 shares issued and 73,986,566 shares outstanding at December 31, 2020. There were 82,601,926 shares issued and 73,601,950 shares outstanding at December 31, 2019. During the year ended December 31, 2020, our Board of Directors declared quarterly cash dividends as follows: Dividends per Common Share Declaration Date Record Date Payable Date $ 0.02 February 10, 2020 March 13, 2020 April 3, 2020 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 and 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. During May of 2020, our Board of Directors determined that it was not in the best interest of our shareholders to issue a dividend for the second quarter of 2020 and they subsequently decided not to issue a dividend for the third or fourth quarters of 2020. The Board of Directors will make determinations regarding future dividends on a quarterly basis using the criteria described above. 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; 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 were no shares of preferred stock issued or outstanding at December 31, 2020 or December 31, 2019. 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. 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. In May 2018, our Board of Directors authorized the repurchase of up to $200 million of our common stock. As of December 31, 2020, we have repurchased a total of 5,036,139 shares of our common stock at an average price of $14.59 and have $126.5 million of remaining availability under this program. We did not make any repurchases of our common stock in 2020. Accumulated Other Comprehensive Income (Loss) Accumulated other comprehensive income (loss) consists of fair value adjustments associated with cash flow hedges, accumulated adjustments for net experience gains or losses and prior service cost related to employee benefit plans and foreign currency translation adjustments, net of tax. The following table presents the changes in accumulated other comprehensive income (loss) by component (in thousands) during the year ended December 31, 2020: For the Year Ended December 31, 2020 Unrealized income (loss) on cash flow hedges Foreign currency translation adjustments Pension and other post-retirement benefits liability Total Beginning Balance $ (3,053) $ (808) $ (15,993) $ (19,854) Other comprehensive income before reclassifications 3,053 1,391 4,537 8,981 Amounts reclassed from accumulated other comprehensive loss — — 2,394 2,394 Ending Balance $ — $ 583 $ (9,062) $ (8,479) Any amounts reclassified from accumulated other comprehensive loss related to cash flow hedges are included in interest expense in our Consolidated Statements of Operations and amounts reclassified related to pension and other post-retirement benefits are included in the computation of net periodic benefit costs at their pre-tax amounts.

Business Combinations

Business Combinations	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
BUSINESS COMBINATIONS	NOTE E—BUSINESS COMBINATIONS Goodwill Goodwill represents the excess of the purchase price over the fair value of the underlying net assets acquired. Trade Names A trade name is a legally protected trade or similar mark. Acquired trade names are valued using an income method approach, generally the relief-from-royalty valuation method. The method uses a royalty rate based on comparable marketplace royalty agreements for similar types of trade names and applies it to the after-tax discounted free cash flow attributed to the trade name. The discount rate used is based on an estimated weighted average cost of capital and the anticipated risk for intangible assets. The valued trade names have an indefinite life based on our plans and expectations for the trade names going forward and are reviewed for impairment under ASC 350-30-35. Intellectual Property and Technology Intellectual property and technology (“IP”) is a design, work or invention that is the result of creativity to which one has ownership rights that may be protected through a patent, copyright, trademark or service mark. IP is valued using the relief from royalty valuation method. The method uses a royalty rate based on comparable market-place royalty agreements for similar types of IP and applies it to the after-tax discounted free cash flow attributed to the IP. The discount rate used is based on an estimated weighted average cost of capital and the anticipated risk for intangible assets. The IP is amortized following the pattern in which the expected benefits will be consumed or otherwise used up over each component’s useful life, based on our plans and expectations for the IP going forward, which is generally the underlying IP’s legal expiration dates. IP is reviewed for impairment under ASC 360-10-35. Customer Relationships Customer relationships are intangible assets that consist of historical and factual information about customers and contacts collected from repeat transactions with customers, with or without any underlying contracts. The information is generally organized as customer lists or customer databases. We have the expectation of repeat patronage from these customers based on the customers’ historical purchase activity, which creates the intrinsic value over a finite period of time and translates into the expectation of future revenue, income, and cash flow. Customer relationships are valued using projected operating income, adjusted for estimated future existing customer growth less estimated future customer attrition, net of charges for net tangible assets, IP charge, trade name charge and work force. The concluded value is the after-tax discounted free cash flow. Customer relationships are reviewed for impairment under ASC 360-10-35. 2020 Acquisition: During the first quarter of 2020, we settled multiple intellectual property and contractual lawsuits involving our SandBox Logistics unit and Arrows Up, LLC. As part of the settlement, SandBox Logistics took control of Arrows Up's existing business, including all equipment and sand logistics contracts, while also receiving a cash payment. We have accounted for the acquisition of Arrows Up, LLC under the acquisition method of accounting in accordance with ASC 805, Business Combinations. Estimates of fair value included in the Consolidated Financial Statements represent our best estimates and valuations. In accordance with the acquisition method of accounting, the fair values are subject to adjustment until we complete our analysis, within a period of time not to exceed one year after the date of acquisition, or March 7, 2021. This business combination resulted in a bargain purchase pursuant to ASC 805-30-25 because no consideration was paid for the fair value of assets acquired and liabilities assumed. The initial fair value of assets acquired, which included cash, accounts receivable, inventories, lease right-of-use assets, and property plant, and equipment, was $20.1 million. The fair value of liabilities assumed, which included lease liabilities and other long-term liabilities, was $2.5 million. An initial gain on bargain purchase of $17.6 million was recorded in "Other income, net, including interest income" in the Condensed Consolidated Statement of Operations. For the year ended December 31, 2020, we recorded a $3.3 million decrease in inventory, a $1.0 million increase to accounts receivable, and a $0.1 million decrease to property, plant and equipment. The total measurement period adjustments for the year ended December 31, 2020 of $2.4 million were recorded as a net decrease to the initial gain on bargain purchase and recorded in "Other (expense) income, net, including interest income" in the Consolidated Statement of Operations. 2018 Acquisition: On May 1, 2018, we completed the acquisition of all of the outstanding capital stock of EP Acquisition Parent, Inc., a Delaware corporation (“EPAP”), and the ultimate parent of EP Minerals, LLC ("EPM"). Contemporaneous with the merger, EPAP was renamed EP Minerals Holdings, Inc. ("EPMH"). The consideration paid consisted of $743.2 million of cash, net of cash acquired of $19.1 million, including $0.5 million of post-closing adjustments. EPM is a global producer of engineered materials derived from industrial minerals, including diatomaceous earth, clay (calcium bentonite and calcium montmorillonite) and perlite. EPM's industrial minerals are used as filter aids, absorbents and functional additives for a variety of industries including food and beverage, biofuels, recreational water, oil and gas, farm and home, landscape, sports turf, paint, plastics, and insecticides. The acquisition of EPM increased our industrial materials product offering in our Industrial & Specialty Products business segment. We have accounted for the acquisition of EPMH under the acquisition method of accounting in accordance with ASC 805, Business Combinations, and have accounted for measurement period adjustments in accordance with ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments. Estimates of fair value included in the Consolidated Financial Statements represent our best estimates and valuations. In accordance with the acquisition method of accounting, the allocation of consideration value was subject to adjustment until we completed our analysis in the second quarter of 2019. The following table sets forth the final allocation of the purchase price to EPMH's identifiable tangible and intangible assets acquired and liabilities assumed, including measurement period adjustments (in thousands): Final allocation of purchase price: Estimate as of December 31, 2018 Measurement Period Adjustments Purchase Price Allocation Accounts receivable, net $ 43,305 $ — $ 43,305 Inventories 86,112 — 86,112 Property, plant and mine development 148,495 (1,937) 146,558 Mineral rights 419,469 (10,580) 408,889 Identifiable intangible assets - finite lived 10,270 (1,500) 8,770 Identifiable intangible assets - indefinite lived 38,050 (1,250) 36,800 Prepaids and deposits 2,072 (245) 1,827 Other assets 7,474 — 7,474 Goodwill 150,628 12,184 162,812 Total assets acquired 905,875 (3,328) 902,547 Accounts payable 13,435 — 13,435 Accrued expenses and other current liabilities 10,304 — 10,304 Deferred tax liabilities 122,811 (3,328) 119,483 Long term obligations 16,076 — 16,076 Total liabilities assumed $ 162,626 $ (3,328) $ 159,298 Net assets acquired $ 743,249 $ — $ 743,249 The acquired intangible assets and the related estimated useful lives consist of the following: Approximate Fair Value Estimated Useful Life (in thousands) (in years) Technology and intellectual property $ 1,400 15 Customer relationships 7,370 15 Total identifiable intangible assets - finite lived $ 8,770 Trade names $ 36,800 Total identifiable intangible assets - indefinite lived $ 36,800 Goodwill represents the excess of the purchase price over the fair value of the underlying net assets acquired. Goodwill in this transaction is attributable to planned growth in our industrial materials product offering in our Industrial & Specialty Products business segment. Intangibles and goodwill are not expected to be deductible for tax purposes. Our Income Statement included revenue of $158.8 million and a net loss of $0.6 million for the year ended December 31, 2018, associated with EPMH following the date of acquisition. We incurred $13.6 million of acquisition-related charges, excluding debt issuance costs, for the year ended December 31, 2018, which are included in selling, general and administrative expenses on our Income Statement. Unaudited Pro Forma Results The results of EPMH's operations have been included in the Consolidated Financial Statements subsequent to the acquisition date. EPMH's fiscal year end was November 30 and the Company's fiscal year end was December 31. Under SEC regulations, if a target's fiscal year end varies by more than 93 days from the acquirer's fiscal year end, it is required to adjust interim periods until it is within 93 days. Since EPMH’s fiscal year end was within 93 days of the Company's fiscal year end, no adjustment is necessary and EPMH’s fiscal year end and interim period ends are used as if they coincided with the Company's fiscal year end and interim period end. The following unaudited pro forma consolidated financial information reflects the results of operations as if the EPMH acquisition had occurred on January 1, 2017, after giving effect to certain purchase accounting adjustments. Material non-recurring transaction costs attributable to the business combination were $15.2 million. Pro forma net income includes incremental interest expense due to the related debt financing, incremental depreciation and depletion expense related to the fair value adjustment of property, plant and mine development, amortization expense related to identifiable intangible assets, and tax expense related to the combined tax provisions. 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 (in thousands, except per share amounts): For the year ended December 31, 2018 2017 Sales $ 1,659,775 $ 1,454,070 Net (loss) income $ (179,220) $ 116,899 Basic (loss) earnings per share $ (2.34) $ 1.44 Diluted (loss) earnings per share $ (2.34) $ 1.43

Accounts Receivable

Accounts Receivable	12 Months Ended
	Dec. 31, 2020
Receivables [Abstract]
ACCOUNTS RECEIVABLE	NOTE F—ACCOUNTS RECEIVABLE At December 31, 2020 and December 31, 2019, accounts receivable (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Trade receivables $ 171,230 $ 178,182 Less: Provision for credit losses (6,604) (8,984) Net trade receivables 164,626 169,198 Other receivables (1) 42,308 13,040 Total accounts receivable $ 206,934 $ 182,238 (1) At December 31, 2020, other receivables included $37.4 million of refunds related to NOL carryback claims filed for various tax years in accordance with certain provisions of the CARES Act. At December 31, 2019, other receivables included $8.1 million of refundable alternative minimum tax credits. We classify our trade receivables into the following portfolio segments: Oil & Gas Proppants and Industrial & Specialty Products, which also aligns with our reporting segments. We estimate the allowance for credit losses based on historical collection trends, the age of outstanding receivables, risks attributable to specific customers, such as credit history, bankruptcy or other going concern issues, and current economic and industry conditions. If events or circumstances indicate that specific receivable balances may be impaired, further consideration is given to the collectability of those balances and the allowance is adjusted accordingly. Past due balances are written off when we have exhausted our internal and external collection efforts and have been unsuccessful in collecting the amount due. The following table reflects the change of the allowance for credit losses (in thousands) during the year ended December 31, 2020, disaggregated by portfolio segments: Oil & Gas Proppants Industrial & Specialty Products Total Beginning balance, December 31, 2019 $ 7,640 $ 1,344 $ 8,984 Provision for credit losses 1,340 170 1,510 Write-offs (3,296) (594) (3,890) Ending balance, December 31, 2020 $ 5,684 $ 920 $ 6,604 Our ten largest customers accounted for approximately 34%, 43% and 48% of total sales during the years ended December 31, 2020, 2019 and 2018, respectively. No single customer accounted for more than 10% of our total sales during the year ended December 31, 2020. Sales to one of our customers accounted for 11% and 15% of our total sales during the years ended December 31, 2019 and 2018, respectively. No other customers accounted for 10% or more of our total sales during the same periods. At December 31, 2020, one of our customers' accounts receivable represented 24% of our total trade accounts receivable, net of allowance. At December 31, 2019, the same customer's accounts receivable represented 12% of our total trade accounts receivable, net of allowance. No other customers accounted for 10% or more of our total trade accounts receivable during the same periods.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2020
Inventory Disclosure [Abstract]
INVENTORIES	NOTE G—INVENTORIES At December 31, 2020 and December 31, 2019, inventories (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Supplies $ 42,329 $ 47,277 Raw materials and work in process 33,723 41,167 Finished goods 28,632 35,988 Total inventories $ 104,684 $ 124,432 The decrease in inventories is primarily attributable to concerted efforts to reduce inventory to improve working capital and impairments of unused inventory at plants we idled. See Note Y - Impairments for additional information.

Property, Plant and Mine Develo

Property, Plant and Mine Development	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND MINE DEVELOPMENT	NOTE H—PROPERTY, PLANT AND MINE DEVELOPMENT At December 31, 2020 and December 31, 2019, property, plant and mine development (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Mining property and mine development $ 788,287 $ 794,899 Asset retirement cost 15,985 18,260 Land 54,710 57,082 Land improvements 76,002 73,203 Buildings 69,841 69,112 Machinery and equipment 1,171,382 1,152,898 Furniture and fixtures 4,071 4,068 Construction-in-progress 27,216 54,675 2,207,494 2,224,197 Accumulated depletion, depreciation, amortization and impairment charges (839,402) (706,610) Total property, plant and mine development, net $ 1,368,092 $ 1,517,587 Depreciation, depletion, and amortization expense related to property, plant and mine development for the years ended December 31, 2020 and 2019 was $143.8 million and $168.6 million, respectively. The amount of interest costs capitalized in property, plant and mine development was $33 thousand and $2.0 million for the years ended December 31, 2020 and 2019, respectively. During the years ended 2020, 2019 and 2018, impairment charges were recorded mainly related to facilities that have reduced capacity or have been idled, including Tyler, Texas, Sparta, Wisconsin, Utica, Illinois, Voca, Texas, Fairchild, Wisconsin, Rochelle, Illinois, Peru, Illinois, and Kosse, Texas. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. See Note Y - Impairments for additional information. On March 21, 2018, we completed the sale of three transload facilities located in the Permian, Eagle Ford, and Marcellus Basins to CIG Logistics (“CIG”) for total consideration of $86.1 million, including the assumption by CIG of $2.2 million of Company obligations. Total cash consideration was $83.9 million. The consideration includes receipt of a vendor incentive from CIG to enter into master transloading service arrangements. Of the total consideration, $25.8 million was allocated to the fair value of the transload facilities, which had a net book value of $20.0 million and resulted in a gain on sale of $5.8 million. The consideration included a related asset retirement obligation of $2.1 million and an equipment note of $0.1 million assumed by CIG. In addition, $60.3 million of the consideration received in excess of the facilities' fair value was allocated to vendor incentives to be recognized as a reduction of costs using a service-level methodology over the contract lives of the transloading service arrangements. At December 31, 2020 and 2019, vendor incentives of $4.8 million and $26.6 million, respectively, were classified in accounts payable and accrued expenses on our balance sheet. Separately, on March 21, 2018, we accrued $7.9 million in contract termination costs for facilities contracts operated by third-parties, which did not transfer to CIG. During the second quarter of 2018, as a result of the final settlement of these contracts, we recorded a $2.7 million credit in selling, general and administrative expenses on our Income Statement. During the years ended 2020 and 2019, management approved the disposal of certain non-operating parcels of land. The assets, which had a combined carrying value of approximately $3.2 million and $1.3 million, respectively, were classified as assets held for sale and were presented within Prepaid expenses and other current assets in the Consolidated Balance Sheets. The proceeds of the disposals were expected to equal or exceed the net carrying value of the assets and, accordingly, no impairment loss was recognized on these assets held for sale. The assets were previously classified as Land, therefore, no adjustments were needed for depreciation of these assets. We disposed of these assets within one year of the balance sheet date. During the fourth quarters of 2020 and 2019, we sold these assets at gains of $0.3 million and $0.6 million, respectively, which were recorded in Other income, net, including interest income in the Consolidated Statements of Operations.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS	NOTE I—GOODWILL AND INTANGIBLE ASSETS The changes in the carrying amount of goodwill (in thousands) by business segment consisted of the following: Oil & Gas Proppants Segment Industrial & Specialty Products Segment Total Balance at December 31, 2018 86,100 175,240 261,340 EPMH acquisition and measurement period adjustment — 12,184 12,184 Balance at December 31, 2019 86,100 187,424 273,524 Impairment losses (86,100) — (86,100) EPMH acquisition adjustment (1) — (1,775) (1,775) Balance at December 31, 2020 $ — $ 185,649 $ 185,649 (1) During the first quarter of 2020, an adjustment was made in accordance with ASC 250 to correct an immaterial error to acquisition accounting. We reclassified $1.8 million between goodwill and deferred tax liabilities. There was no impact to the Consolidated Statements of Operations. Goodwill and trade names are evaluated for impairment annually as of October 31, or more frequently when indicators of impairment exist. We evaluated events and circumstances since the date of our last qualitative assessment, including macroeconomic conditions, industry and market conditions, and our overall financial performance. As a result of triggering events identified during the years ended 2020 and 2018 we performed a quantitative analysis. The fair value of our reporting units was determined using a combination of the discounted cash flow method and the market multiples approach. As a result of this analysis we determined that the goodwill was impaired. We recognized goodwill impairment charges of $86.1 million and $164.2 million, respectively. No impairments were recorded related to goodwill during the year ended 2019. These impairment charges related to our Oil & Gas Proppants segment and were recorded in the "Goodwill and other asset impairments" caption of our Consolidated Statements of Operations. See Note Y - Impairments for additional information. The changes in the carrying amount of intangible assets (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Gross Carrying Amount Accumulated Amortization Impairments Net Gross Carrying Amount Accumulated Amortization Impairments Net Technology and intellectual property $ 71,052 $ (18,854) (1,373) $ 50,825 $ 86,183 $ (17,080) — $ 69,103 Customer relationships 66,999 (23,182) $ — 43,817 68,599 (18,737) (1,240) 48,622 Total definite-lived intangible assets: $ 138,051 $ (42,036) $ (1,373) $ 94,642 $ 154,782 $ (35,817) $ (1,240) $ 117,725 Trade names 65,390 — (1,150) 64,240 65,390 — — 65,390 Other 700 — — 700 700 — — 700 Total intangible assets: $ 204,141 $ (42,036) $ (2,523) $ 159,582 $ 220,872 $ (35,817) $ (1,240) $ 183,815 During the years ended 2020, 2019, and 2018, we recorded impairments related to trade names, technology and intellectual property, and customer relationships. See Note Y - Impairments for additional information. Estimated useful life of technology and intellectual property is 15 years. Estimated useful life of customer relationships is a range of 13 - 20 years. During the second quarter of 2020, we expensed $11.8 million of capitalized legal fees related to the unsuccessful defense of a small number of our patents. These charges related to the Oil & Gas Proppants segment and were recorded in Selling, general, and administrative expense in the Consolidated Statement of Operations. During the first quarter of 2019, measurement period adjustments related to the Company's EPMH acquisition decreased the gross carrying amounts of the technology and intellectual property by $1.5 million and the trade names by $1.3 million. See Note E - Business Combinations. Amortization expense was $10.3 million, $10.8 million and $9.7 million for the years ended December 31, 2020, 2019, and 2018, respectively. The estimated amortization expense related to definite-lived intangible assets (in thousands) for the five succeeding years is as follows: 2021 $ 9,623 2022 $ 9,608 2023 $ 9,603 2024 $ 9,605 2025 $ 9,603

Accounts Payable and Accrued Li

Accounts Payable and Accrued Liabilities	12 Months Ended
	Dec. 31, 2020
Payables and Accruals [Abstract]
ACCOUNTS PAYABLE AND ACCRUED LIABILITIES	NOTE J—ACCOUNTS PAYABLE AND ACCRUED LIABILITIES At December 31, 2020 and 2019, accounts payable and accrued liabilities (in thousands) consisted of the following: December 31, 2020 2019 Trade payables $ 90,564 $ 181,029 Accrued salaries and wages 7,432 12,385 Accrued vacation liability 2,499 3,053 Current portion of liability for pension and post-retirement benefits 1,338 2,993 Accrued healthcare liability 1,886 4,078 Accrued property taxes and sales taxes 5,136 4,070 Vendor incentives 4,782 26,617 Other accrued liabilities 8,283 14,012 Accounts payable and accrued liabilities $ 121,920 $ 248,237 Other accrued liabilities consist of employer related expenses, royalties payable, accrued interest payable, and other items.

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
DEBT	NOTE K—DEBT At December 31, 2020 and 2019, debt (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Senior secured credit facility: Revolver expiring May 1, 2023 (4.19% at December 31, 2020 and 7.75% at December 31, 2019) $ 25,000 $ — Term Loan facility—final maturity May 1, 2025 (5.00% at December 31, 2020 and 5.81% December 31, 2019) 1,234,800 1,247,600 Less: Unamortized original issue discount (4,376) (5,412) Less: Unamortized debt issuance cost (20,259) (25,390) Note payable secured by royalty interest — 10,438 Insurance financing notes payable 4,187 5,055 Equipment notes payable — 87 Finance leases 350 70 Total debt 1,239,702 1,232,448 Less: current portion (42,042) (18,463) Total long-term portion of debt $ 1,197,660 $ 1,213,985 Senior Secured Credit Facility On May 1, 2018, we entered into a Third Amended and Restated Credit Agreement (the "Credit Agreement"), which increased our existing senior debt by entering into a new $1.380 billion senior secured Credit Facility, consisting of a $1.280 billion term loan (the "Term Loan") and a $100 million revolving credit facility (the "Revolver") (collectively the "Credit Facility") that may also be used for swingline loans or letters of credit, and we may elect to increase the term loan in accordance with the terms of the Credit Agreement. Borrowings under the Credit Agreement will bear interest at variable rates as determined at our election, at LIBOR or a base rate, in each case, plus an applicable margin. In addition, under the Credit Agreement, we are required to pay a per annum facility fee and fees for letters of credit. The Credit Agreement is secured by substantially all of our assets and of our domestic subsidiaries' assets and a pledge of the equity interests in such entities. The Term Loan matures on May 1, 2025, and the Revolver expires on May 1, 2023. We capitalized $38.7 million in debt issuance costs and original issue discount as a result of the new Credit Agreement. The Credit Agreement contains covenants that, among other things, limit our ability, and certain of our subsidiaries' abilities, to create, incur or assume indebtedness and liens, to make acquisitions or investments, to sell assets and to pay dividends. The Credit Agreement also requires us to maintain a consolidated 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 30% of the Revolver commitment. These covenants are subject to a number of important exceptions and qualifications. The Credit Agreement includes events of default and other affirmative and negative covenants that are usual for facilities and transactions of this type. As of December 31, 2020 and 2019, we are in compliance with all covenants in accordance with our senior secured Credit Facility. Term Loan At December 31, 2020, contractual maturities of our senior secured Credit Facility (in thousands) are as follows: 2021 $ 12,800 2022 12,800 2023 12,800 2024 12,800 2025 1,183,600 Thereafter — Total $ 1,234,800 During the third quarter of 2019, we repurchased outstanding debt under the Term Loan in the amount of $10 million at a rate of 95.5%. Debt issuance costs and original issue discount were recalculated with the reduced future debt payments, and additional costs of approximately $0.4 million were expensed. As a result, we recorded a gain on extinguishment of debt in the amount of $0.1 million. The gain on extinguishment was recorded in Other income, net, including interest income in the Consolidated Statements of Operations. Revolving Line-of-Credit We have a $100.0 million Revolver with $25.0 million drawn and $23.0 million allocated for letters of credit as of December 31, 2020, leaving $52.0 million available under the Revolver. We have the intent and ability to repay the amounts outstanding on the Revolver within one year, therefore, the outstanding balance as of December 31, 2020 was classified as current. Based on our consolidated leverage ratio of 6.07:1.00 as of December 31, 2020, we may draw up to $30.0 million without the consent of our lenders. With the consent of our lenders, we have access to the full availability of the Revolver. Note Payable Secured by Royalty Interest In conjunction with the acquisition of New Birmingham, Inc. in August 2016, we assumed a note payable secured by a royalty interest. The monthly royalty payment is calculated based on future tonnages and sales related to the sand shipped from our Tyler, Texas facility. The note payable is due by June 30, 2032. The note does not provide a stated interest rate. The royalty note payable fair value was estimated to be $22.5 million on the acquisition date. The estimate was made using a discounted cash flow model, which calculated the present value of projected future cash payments required under the agreement using a discounted rate of 14%. During the fourth quarter of 2020, we executed an amendment to the note payable which settled the outstanding balance in its entirety in exchange for a one-time payment of $2.55 million. Future royalties may be owed under this amended agreement if we resume production at our Tyler facility, however, we have no such plans to resume production in the near term. Therefore, no amounts have been accrued. The settlement of the note payable resulted in a gain of $8.3 million which was recorded in Other income, net, including interest income in the Consolidated Statements of Operations. Gains in the amount of $16.9 million were recorded during 2019 as a result of a change in estimate of future tonnages and sales related to the sand shipped from the Tyler facility. Insurance Financing Notes Payable During the third quarter of 2020, we renewed our insurance policies and financed the payments through notes payable with a stated interest rate of 3.0%. These payments will be made in installments throughout a nine-month period and, as such, have been classified as current debt. As of December 31, 2020, the notes payable had a balance of $4.2 million.

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]
ASSET RETIREMENT OBLIGATIONS	NOTE L—ASSET RETIREMENT OBLIGATIONS Mine reclamation 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 December 31, 2020 and 2019, we had a liability of $24.7 million and $25.8 million, respectively, in other long-term obligations related to our asset retirement obligations. Changes in the asset retirement obligations (in thousands) during the years ended December 31, 2020 and 2019 are as follows: December 31, 2020 December 31, 2019 Beginning balance $ 25,825 $ 18,413 Accretion 1,434 1,531 Additions and revisions of estimates (2,542) 5,881 Ending balance $ 24,717 $ 25,825

Fair Value Accounting

Fair Value Accounting	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
FAIR VALUE ACCOUNTING	NOTE M—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, quoted 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 December 31, 2020 and 2019, approximate their reported carrying values. 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. Changes in the fair value of the royalty note payable utilize Level 3 inputs, such as estimates of future tonnages sold and average sales price. See Note K - Debt for more information on the change in fair value during the year ended December 31, 2020. As a result of the settlement of this royalty note payable in its entirety during the fourth quarter, the outstanding balance as of December 31, 2020 was zero. Derivative Instruments The estimated fair value of our derivative instruments 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.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE INSTRUMENTS	NOTE N—DERIVATIVE INSTRUMENTS Cash Flow Hedges of Interest Rate Risk We enter into interest rate swap agreements in connection with our Term Loan facility to add stability to interest expense and to manage our exposure to interest rate movements. The derivative instruments are recorded on the balance sheet within other current or long-term assets or liabilities based on maturity dates at their fair values. As of December 31, 2020, the fair values of our interest rate swaps were both zero as our swap agreements matured on July 31, 2020. At December 31, 2019, the fair values of our two interest rate swaps were a liability of $2.8 million and a liability of $1.3 million and were classified within other long-term liabilities on our balance sheet. We have designated the interest rate swap agreements as qualified cash flow hedges. Accordingly, the effective portion of the gain or loss on the derivative instrument is reported as a component of other comprehensive income and recognized in earnings in the same period or periods during which the hedged transaction affects earnings. The following table summarizes the fair value of our derivative instruments (in thousands, except contract/notional amount). See Note M - Fair Value Accounting for more information regarding the estimated fair values of our derivative instruments at December 31, 2020 and 2019. December 31, 2020 December 31, 2019 Maturity Contract/Notional Carrying Fair Maturity Date Contract/Notional Carrying Fair LIBOR (1) interest rate swap agreement 2020 $440 million $ — $ — 2020 $440 million $ (2,768) $ (2,768) LIBOR (1) interest rate swap agreement 2020 $200 million $ — $ — 2020 $200 million $ (1,259) $ (1,259) (1) Agreements fix the LIBOR interest rate base to 2.74% On May 1, 2018, as a result of entering into the new Credit Agreement, we determined the existing interest rate cap derivative no longer qualified for hedge accounting. During the year ended December 31, 2019 we recognized $76 thousand of deferred losses in accumulated other comprehensive loss into earnings. During the year ended December 31, 2020, we had no ineffectiveness for the interest rate swap derivatives. The following table summarizes the effect of derivative instruments (in thousands) on our income statements and our consolidated statements of comprehensive income for the years ended December 31, 2020, 2019 and 2018: 2020 2019 2018 Deferred losses from derivatives in OCI, beginning of period $ (3,053) $ (1,621) $ (76) Gain (loss) recognized in OCI from derivative instruments 3,053 (1,432) (1,622) Loss reclassified from Accumulated OCI — — 77 Deferred losses from derivatives in OCI, end of period $ — $ (3,053) $ (1,621)

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
EQUITY-BASED COMPENSATION	NOTE O—EQUITY-BASED COMPENSATION In July 2011, we adopted the U.S. Silica Holdings, Inc. 2011 Incentive Compensation Plan (the “2011 Plan”), which was amended and restated in May 2015 and amended and restated effective February 1, 2020. The 2011 Plan provides for grants of stock options, restricted stock, performance share units and other incentive-based awards. We believe our 2011 Plan aligns the interests of our employees and directors with those of our common stockholders. At December 31, 2020, we have 3,752,317 shares of common stock that may be issued under the 2011 Plan. We use a combination of treasury stock and new shares if necessary to satisfy option exercises or vesting of restricted awards and performance share units. Stock Options The following table summarizes the status of, and changes in, our stock option awards during the year ended December 31, 2020: Number of Weighted Aggregate Intrinsic Value Weighted Outstanding at December 31, 2019 826,658 $ 28.97 $ 11,557 4.1 years Granted — — — Exercised — — — Forfeited (443) 32.41 — Expired — $ — $ — Outstanding at December 31, 2020 826,215 $ 29.05 $ — 3.1 years Exercisable at December 31, 2020 826,215 $ 29.05 $ — 3.1 years There were no grants of stock options during the years ended December 31, 2020, 2019 and 2018. There were zero, 10,000 and 4,167 stock options exercised during the years ended December 31, 2020, 2019 and 2018, respectively. The total intrinsic value of stock options exercised was zero, $12 thousand and $0.1 million for the years ended December 31, 2020, 2019 and 2018, respectively. Cash received from stock options exercised during the years ended December 31, 2020, 2019 and 2018 was zero, $0.1 million and $0.1 million, respectively. The tax benefit realized from stock option exercises was zero, $3 thousand and $14 thousand for the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020 and 2019, there was no unrecognized compensation expense related to these options. We recognized $1.4 million of equity-based compensation expense related to options during the year ended December 31, 2018. We account for forfeitures as they occur. Restricted Stock and Restricted Stock Unit Awards The following table summarizes the status of, and changes in, our unvested restricted stock awards during the year ended December 31, 2020: Number of Shares Grant Date Weighted Unvested, December 31, 2019 1,020,248 $ 15.86 Granted 1,590,170 4.09 Vested (539,614) 15.98 Forfeited (290,978) 10.66 Unvested, December 31, 2020 1,779,826 $ 6.22 We granted 1,590,170, 814,387 and 415,110 restricted stock and restricted stock unit awards during the years ended December 31, 2020, 2019 and 2018, respectively. The fair value of the awards was based on the market price of our stock at date of grant. We recognized $8.1 million, $8.2 million and $7.6 million of equity-based compensation expense related to restricted stock awards during the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020, there was $6.6 million of unrecognized compensation expense related to these restricted stock awards, which is expected to be recognized over a weighted-average period of 1.6 years. We also granted 335,039 awards, which included 58,246 forfeited and partially vested awards, during the year ended December 31, 2020. These awards will vest over a period of three years and will be settled in cash. As such, these awards have been classified as liability instruments. We recognized $0.6 million of expense related to these awards for the year ended December 31, 2020. The liability for these awards is included in accounts payable and other accrued expenses on our balance sheets. These awards will be remeasured at fair value each reporting period with resulting changes reflected in our income statements. Estimated unrecognized expense related to these awards is $1.4 million over a period of 2.1 years. Performance Share Unit Awards The following table summarizes the status of, and changes in, our performance share unit awards during the year ended December 31, 2020: Number of Shares Grant Date Weighted Unvested, December 31, 2019 838,722 $ 18.00 Granted 1,020,161 6.57 Vested — — Forfeited/Cancelled (345,235) 24.23 Unvested, December 31, 2020 1,513,648 $ 12.36 We granted 1,020,161, 607,130 and 261,500 of performance share unit awards during the years ended December 31, 2020, 2019 and 2018, respectively. The grant date weighted average fair value of these awards was estimated to be $6.57, $15.58 and $31.24 for the years ended December 31, 2020, 2019 and 2018, respectively, and the number of units that will vest will depend on the percentage ranking of the Company's total shareholder return ("TSR") compared to the TSR for each of the companies in the peer group over the three year period from January 1, 2020 through December 31, 2022 for the 2020 grant, January 1, 2019 through December 31, 2021 for the 2019 grant, and from January 1, 2018 through December 31, 2020 for the 2018 grant. The related compensation expense is recognized on a straight-line basis over the vesting period. The grant date fair value for these awards was estimated using a Monte Carlo simulation model. The Monte Carlo simulation model requires the use of highly subjective assumptions. Our key assumptions in the model included the price and the expected volatility of our common stock and our self-determined peer group companies’ stock, risk-free rate of interest, dividend yields and cross-correlations between our common stock and our self-determined peer group companies' stock. We recognized $6.8 million, $7.7 million and $13.3 million of compensation expense related to performance share unit awards during the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020, there was $6.1 million of unrecognized compensation expense related to these performance share unit awards, which is expected to be recognized over a weighted-average period of 1.7 years. We also granted cash awards during the year ended December 31, 2020. These awards will vest over a period of three years and will be settled in cash. As such, these awards have been classified as liability instruments. We recognized $0.9 million of expense related to these awards for the year ended December 31, 2020. The liability for these awards is included in accounts payable and other accrued expenses on our balance sheets. These awards will be remeasured at fair value each reporting period with resulting changes reflected in our income statements. Estimated unrecognized expense related to these awards is $1.3 million over a period of 2.1 years.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	NOTE P—COMMITMENTS AND CONTINGENCIES Future Minimum Annual Commitments at December 31, 2020 (in thousands): Year ending December 31, Minimum Purchase Commitments 2021 $ 14,812 2022 10,328 2023 10,328 2024 7,020 2025 2,654 Thereafter 6,604 Total future purchase commitments $ 51,746 Minimum Purchase Commitments We enter into service agreements with our transload 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. Contingent Liability on Royalty Agreement On May 17, 2017, we purchased reserves in Crane County, Texas, for $94.4 million cash consideration plus contingent consideration. The contingent consideration is a royalty that is based on the tonnage shipped to third-parties. Because the contingent consideration is dependent on future tonnage sold, the amounts of which are uncertain, it is not currently possible to estimate the fair value of these future payments. The contingent consideration will be capitalized at the time a payment is probable and reasonably estimable, and the related depletion expense will be adjusted prospectively. 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 years ended December 31, 2020, 2019 and 2018, one, one and twenty claims, respectively, were brought against U.S. Silica. As of December 31, 2020, there were 52 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. 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 December 31, 2020 and 2019, other non-current assets included zero for insurance for third-party products liability claims and other long-term obligations included $1.0 million and $0.9 million, respectively, for third-party products liability claims. Obligations Under Guarantees

Pension and Post-Retirement Ben

Pension and Post-Retirement Benefits	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
PENSION AND POST-RETIREMENT BENEFITS	NOTE Q— PENSION AND POST-RETIREMENT BENEFITS We maintain a single-employer noncontributory defined benefit pension plan covering certain employees. The plan is frozen to all new employees. The plan provides benefits based on each covered employee’s years of qualifying service. Our funding policy is to contribute amounts within the range of the minimum required and maximum deductible contributions for the plan consistent with a goal of appropriate minimization of the unfunded projected benefit obligations. The pension plan uses a benefit level per year of service for covered hourly employees and a final average pay method for covered salaried employees. The plan uses the projected unit credit cost method to determine the actuarial valuation. We employ a total rate of return investment approach whereby a mix of equities and fixed income investments are used to maximize the long-term return of plan assets for a prudent level of risk. Risk tolerance is established through careful consideration of plan liabilities, plan funded status, and corporate financial condition. The investment portfolio contains a diversified blend of equity and fixed-income investments. Furthermore, equity investments are diversified across U.S. and non-U.S. stocks, as well as growth, value and small and large capitalizations. Investment risk is measured and monitored on an ongoing basis through quarterly investment portfolio reviews, annual liability measurements, and periodic asset/liability studies. We employ a building block approach in determining the long-term rate of return for plan assets. Historical markets are studied and long-term historical relationships between equities and fixed-income are preserved consistent with the widely accepted capital market principle that assets with higher volatility generate a greater return over the long run. Current market factors such as inflation and interest rates are evaluated before long-term capital market assumptions are determined. The long-term portfolio return is established via a building block approach with proper consideration of diversification and rebalancing. Peer data and historical returns are reviewed to check for reasonability and appropriateness. In addition, we provide defined benefit post-retirement health care and life insurance benefits to some employees. Covered employees become eligible for these benefits at retirement after meeting minimum age and service requirements. The projected future cost of providing post-retirement benefits, such as healthcare and life insurance, is recognized as an expense as employees render services. In general, retiree health benefits are paid as covered expenses are incurred. Net pension benefit cost (in thousands) consisted of the following for the years ended December 31, 2020, 2019 and 2018: Year Ended 2020 2019 2018 Service cost $ 2,253 $ 1,304 $ 1,307 Interest cost 4,037 5,375 4,632 Expected return on plan assets (6,019) (6,171) (5,969) Net amortization and deferral 3,127 1,648 2,526 Net pension benefit costs $ 3,398 $ 2,156 $ 2,496 Net post-retirement benefit cost (in thousands) consisted of the following for the years ended December 31, 2020, 2019 and 2018: Year Ended December 31, 2020 2019 2018 Service cost $ 70 $ 88 $ 102 Interest cost 584 789 740 Unrecognized net (gain)/loss — (29) — Net post-retirement benefit costs $ 654 $ 848 $ 842 The changes in benefit obligations and plan assets (in thousands), as well as the funded status (in thousands) of our pension and post-retirement plans at December 31, 2020 and 2019 are as follows: Pension Benefits Post-retirement Benefits 2020 2019 2020 2019 Benefit obligation at January 1, $ 148,491 $ 138,900 $ 22,054 $ 21,570 Service cost 2,253 1,304 70 88 Interest cost 4,037 5,375 584 789 Actuarial (gain) loss 11,119 17,225 1,329 206 Benefits paid (8,649) (14,922) (1,751) (815) Other (1) (53) 609 (10,968) 216 Benefit obligation at December 31, $ 157,198 $ 148,491 $ 11,318 $ 22,054 Fair value of plan assets at January 1, $ 110,431 $ 102,396 $ — $ — Actual return on plan assets 13,306 17,919 — — Employer contributions 5,475 4,755 1,335 599 Benefits paid (8,649) (14,922) (1,751) (815) Other (1) — 283 416 216 Fair value of plan assets at December 31, $ 120,563 $ 110,431 $ — $ — Plan assets less than benefit obligations at December 31 recognized as liability for pension and other post-retirement benefits $ (36,635) $ (38,060) $ (11,318) $ (22,054) (1) Includes opening pension benefit obligation and plan assets balances related to the May 1, 2018, EPMH acquisition The accumulated benefit obligation for the defined benefit pension plans, which excludes the assumption of future salary increases, totaled $157.2 million and $148.5 million at December 31, 2020 and 2019, respectively. We also sponsor unfunded, nonqualified pension plans. The projected benefit obligation, accumulated benefit obligation and fair value of plan assets for these plans were $1.6 million, $1.6 million and zero, respectively, at December 31, 2020 and $1.6 million, $1.6 million and zero, respectively, at December 31, 2019. Future estimated annual benefit payments (in thousands) for pension and post-retirement benefit obligations at December 31, 2020 are as follows: Benefits Post-retirement Pension Before After 2021 $ 9,329 $ 1,217 $ 1,217 2022 9,346 1,095 1,095 2023 9,326 1,002 1,002 2024 9,678 959 959 2025 9,224 883 883 2026-2030 44,832 3,393 3,393 Our best estimate of expected contributions to the pension and post-retirement medical benefit plans for the 2021 fiscal year are $5.3 million and $1.2 million, respectively. The total amounts in accumulated other comprehensive income (loss) related to net actuarial loss, net of tax, for the pension and post-retirement plans were $24.7 million and $22.1 million as of December 31, 2020 and 2019, respectively. The total amounts in accumulated other comprehensive income (loss) related to prior service cost, net of tax, for the pension and post-retirement plans, was a loss of $9.4 million and income of $2.2 million as of December 31, 2020 and 2019, respectively. The actuarial losses in 2020 and 2019 were primarily driven by the change in discount rates on the U.S. qualified plan and Postretirement Medical plans. The impact of the discount rate change was partially offset by the actual return on plan assets exceeding the expected return on plan assets. Additionally, the Society of Actuaries released an updated mortality table projection scale for measurement of retirement program obligations in both 2020 and 2019. The impact of the mortality table changes provided a partial offset of the impact of the discount rate change. The following weighted-average assumptions were used to determine our obligations under the plans: Pension Benefits Post-retirement Benefits 2020 2019 2020 2019 Discount rate 2.5 % 3.2 % 2.1 % 3.2 % Long-term rate of compensation increase 3.0% 3.0%-3.5% N/A N/A Long-term rate of return on plan assets 6.3 % 6.3% N/A N/A Health care cost trend rate: Pre-65 initial rate/ultimate rate N/A N/A 6.5%/4.5% 7.0%/4.5% Pre-65 ultimate year N/A N/A 2028 2026 Post-65 initial rate/ultimate rate N/A N/A 7.0%/4.5% 7.5%/4.5% Post-65 ultimate year N/A N/A 2028 2027 The weighted average discount rates used to determine the projected pension and post-retirement obligations were updated to reflect the expected long-term rates of return with maturities comparable to payments for the plan obligations utilizing Aon Hewitt's AA Above Medium Curve. Mortality tables used for pension benefits and post-retirement benefits plans are the following: Pension and Post-retirement Benefits 2020 2019 Healthy Lives Pri-2012 base mortality tables with generational mortality improvements using Scale MP-2020 Pri-2012 base mortality tables with generational mortality improvements using Scale MP-2019 Disabled Lives Pri-2012 base mortality tables with generational mortality improvements using Scale MP-2020 Pri-2012 base mortality tables with generational mortality improvements using Scale MP-2019 The major investment categories and their relative percentage of the fair value of total plan assets as invested at December 31, 2020, and 2019 were as follows: Pension Benefits Post-retirement Benefits (1) 2020 2019 2020 2019 Equity securities 57.9 % 52.1 % — % — % Debt securities 41.3 % 46.6 % — % — % Cash 0.8 % 1.3 % — % — % (1) Retiree health benefits are paid by the Company as covered expenses are incurred. The fair values of the pension plan assets (in thousands) at December 31, 2020, by asset category, were as follows: Level 1 Level 2 Level 3 Total Cash and cash equivalents $ — $ 1,020 $ — $ 1,020 Mutual funds: Diversified emerging markets 7,064 — — 7,064 Foreign large blend 22,638 — — 22,638 Large-cap blend 22,272 — — 22,272 Mid-cap blend 12,972 — — 12,972 Real estate 4,822 — — 4,822 Fixed income securities: Corporate notes and bonds 38,983 — — 38,983 U.S. Treasuries 8,582 — — 8,582 Mortgage-backed securities — 1,780 — 1,780 Asset-backed securities — 430 — 430 Net asset $ 117,333 $ 3,230 $ — $ 120,563 The fair values of the pension plan assets (in thousands) at December 31, 2019, by asset category, were as follows: Level 1 Level 2 Level 3 Total Cash and cash equivalents $ — $ 1,385 $ — $ 1,385 Mutual funds: Diversified emerging markets 4,942 — — 4,942 Foreign large blend 19,183 — — 19,183 Large-cap blend 20,738 — — 20,738 Mid-cap blend 8,416 — — 8,416 Real estate 4,309 — — 4,309 Fixed income securities: Corporate notes and bonds 37,664 — — 37,664 U.S. Treasuries 10,894 — — 10,894 Mortgage-backed securities — 2,496 — 2,496 Asset-backed securities — 404 — 404 Net asset $ 106,146 $ 4,285 $ — $ 110,431 We contribute to three multiemployer defined benefit pension plans under the terms of collective-bargaining agreements for union-represented employees. A multiemployer plan is subject to collective bargaining for employees of two or more unrelated companies. These plans allow multiple employers to pool their pension resources and realize efficiencies associated with the daily administration of the plan. Multiemployer plans are generally governed by a board of trustees composed of management and labor representatives and are funded through employer contributions. However, in most cases, management is not directly represented. The risks of participating in multiemployer plans differ from single employer plans as follows: 1) assets contributed to a multiemployer plan by one employer may be used to provide benefits to employees of other participating employers, 2) if a participating employer stops contributing to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers, and 3) if we cease to have an obligation to contribute to one or more of the multiemployer plans to which we contribute, we may be required to pay those plans an amount based on the underfunded status of the plan, referred to as a withdrawal liability. A summary of each multiemployer pension plan for which we participate is presented below: Pension EIN/ Pension Pension Protection Act Zone Status (1) FIP/RP Status Company Surcharge Expiration 2020 2019 2020 2019 2018 LIUNA 52-6074345/001 Green Red No $ 361 $ 385 $ 573 No 6/4/2022 IUOE 36-6052390/001 Green Green No 256 310 1,385 No 7/31/2022 CSSS (2) 36-6044243/001 Red Red Yes 51 51 51 NA NA (1) The Pension Protection Act of 2006 defines the zone status as follows: green—healthy, yellow—endangered, orange—seriously endangered and red—critical. (2) In 2011, we withdrew from the Central States, Southeast and Southwest Areas Pension Plan. The withdrawal liability of $1.0 million will be paid in monthly installments of $4,000 until 2031. Our contributions to individual multiemployer pension funds did not exceed 5% of the fund’s total contributions for the years ended December 31, 2020, 2019 and 2018. Additionally, our contributions to multiemployer post-retirement benefit plans were immaterial for all periods presented in the accompanying consolidated financial statements. We also sponsor a defined contribution plan covering certain employees. We contribute to the plan in two ways. For certain employees not covered by the defined benefit plan, we make a contribution equal to 4% of their salary. For all other eligible employees, we make a contribution of up to 6% of eligible earnings. Contributions were $3.5 million, $6.1 million and $2.6 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	NOTE R— LEASES We lease railroad cars, office space, mining property, mining/processing equipment, and transportation and other equipment. The majority of our leases have remaining lease terms of one year to 20 years. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. We have lease agreements with lease and non-lease components, the latter of which are generally accounted for separately. Supplemental balance sheet information related to leases (in thousands except for term and rate information) was as follows: Leases Classification December 31, 2020 December 31, 2019 Assets Operating Operating lease right-of-use assets $ 37,469 $ 53,098 Finance Property, plant and mine development, net 339 — Total leased assets $ 37,808 $ 53,098 Liabilities Current Operating Current portion of operating lease liabilities $ 17,388 $ 53,587 Finance Current portion of long-term debt 55 — Non-Current Operating Operating lease liabilities 76,361 117,964 Finance Long-term debt, net 295 — Total lease liabilities $ 94,099 $ 171,551 We recorded impairment charges related to railcar leases, various equipment leases and an office building lease. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. See Note Y - Impairments for additional information. During the year ended 2020, we received lease concessions from certain lessors. Based on accounting elections provided by the FASB and in accordance with ASC 842-10, we have not accounted for these concessions as lease modifications. Based on remeasurement of the amended leases, for the year ended December 31, 2020, we recorded a decrease to the ROU assets of $1.0 million and a decrease to the liability of $25.0 million. A gain of $24.0 million was recognized as operating income through cost of goods sold in our consolidated income statement for the year ended December 31, 2020. Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. As most of our leases do not provide an implicit rate, in determining the lease liability and the present value of lease payments, we used our incremental borrowing rate based on the information available at the lease commencement date. The weighted average remaining lease term and discount rate as of December 31, 2020 and 2019 related to leases are as follows: Lease Term and Discount Rate December 31, 2020 December 31, 2019 Weighted average remaining lease term: Operating leases 6.9 years 4.5 years Finance leases 2.9 years N/A Weighted average discount rate: Operating leases 5.8 % 5.7 % Finance leases 5.0 % — % The components of lease expense included in our Consolidated Statements of Operations were as follows: Lease Costs Classification Year Ended Year Ended Operating lease costs (1) Cost of Sales $ 26,548 88,966 Operating lease costs (2) Selling, general, and administrative 1,808 3,993 Right-of-use asset impairment Goodwill and other asset impairments 3,406 115,443 Total (3) $ 31,762 208,402 (1) Includes short-term operating lease costs of $9.6 million and $18.2 million for the years ended December 31, 2020 and 2019, respectively. (2) Includes short-term operating lease costs of $0.4 million and $0.7 million for the years ended December 31, 2020 and 2019, respectively. (3) Does not include expense for the year ended December 31, 2020 of $12 thousand for finance leases. Supplemental cash flow information related to leases was as follows: Year Ended December 31, 2020 Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 62,140 $ 74,740 Operating cash flows for finance leases $ 12 $ — Right-of-use assets obtained in exchange for new lease liabilities: Operating leases $ 10,747 $ 232,123 Finance leases $ 359 $ — Maturities of lease liabilities as of December 31, 2020: Maturities of lease liabilities Operating leases Finance leases 2021 $ 23,217 $ 71 2022 16,447 71 2023 16,019 244 2024 14,181 — 2025 11,617 — Thereafter 38,205 — Total lease payments $ 119,686 386 Less: Interest 20,984 36 Less: Other operating expenses 4,953 — Total $ 93,749 350
Leases	NOTE R— LEASES We lease railroad cars, office space, mining property, mining/processing equipment, and transportation and other equipment. The majority of our leases have remaining lease terms of one year to 20 years. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. We have lease agreements with lease and non-lease components, the latter of which are generally accounted for separately. Supplemental balance sheet information related to leases (in thousands except for term and rate information) was as follows: Leases Classification December 31, 2020 December 31, 2019 Assets Operating Operating lease right-of-use assets $ 37,469 $ 53,098 Finance Property, plant and mine development, net 339 — Total leased assets $ 37,808 $ 53,098 Liabilities Current Operating Current portion of operating lease liabilities $ 17,388 $ 53,587 Finance Current portion of long-term debt 55 — Non-Current Operating Operating lease liabilities 76,361 117,964 Finance Long-term debt, net 295 — Total lease liabilities $ 94,099 $ 171,551 We recorded impairment charges related to railcar leases, various equipment leases and an office building lease. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. See Note Y - Impairments for additional information. During the year ended 2020, we received lease concessions from certain lessors. Based on accounting elections provided by the FASB and in accordance with ASC 842-10, we have not accounted for these concessions as lease modifications. Based on remeasurement of the amended leases, for the year ended December 31, 2020, we recorded a decrease to the ROU assets of $1.0 million and a decrease to the liability of $25.0 million. A gain of $24.0 million was recognized as operating income through cost of goods sold in our consolidated income statement for the year ended December 31, 2020. Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. As most of our leases do not provide an implicit rate, in determining the lease liability and the present value of lease payments, we used our incremental borrowing rate based on the information available at the lease commencement date. The weighted average remaining lease term and discount rate as of December 31, 2020 and 2019 related to leases are as follows: Lease Term and Discount Rate December 31, 2020 December 31, 2019 Weighted average remaining lease term: Operating leases 6.9 years 4.5 years Finance leases 2.9 years N/A Weighted average discount rate: Operating leases 5.8 % 5.7 % Finance leases 5.0 % — % The components of lease expense included in our Consolidated Statements of Operations were as follows: Lease Costs Classification Year Ended Year Ended Operating lease costs (1) Cost of Sales $ 26,548 88,966 Operating lease costs (2) Selling, general, and administrative 1,808 3,993 Right-of-use asset impairment Goodwill and other asset impairments 3,406 115,443 Total (3) $ 31,762 208,402 (1) Includes short-term operating lease costs of $9.6 million and $18.2 million for the years ended December 31, 2020 and 2019, respectively. (2) Includes short-term operating lease costs of $0.4 million and $0.7 million for the years ended December 31, 2020 and 2019, respectively. (3) Does not include expense for the year ended December 31, 2020 of $12 thousand for finance leases. Supplemental cash flow information related to leases was as follows: Year Ended December 31, 2020 Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 62,140 $ 74,740 Operating cash flows for finance leases $ 12 $ — Right-of-use assets obtained in exchange for new lease liabilities: Operating leases $ 10,747 $ 232,123 Finance leases $ 359 $ — Maturities of lease liabilities as of December 31, 2020: Maturities of lease liabilities Operating leases Finance leases 2021 $ 23,217 $ 71 2022 16,447 71 2023 16,019 244 2024 14,181 — 2025 11,617 — Thereafter 38,205 — Total lease payments $ 119,686 386 Less: Interest 20,984 36 Less: Other operating expenses 4,953 — Total $ 93,749 350

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
INCOME TAXES	NOTE S— INCOME TAXES We evaluate our deferred tax assets periodically to determine if valuation allowances are required. Ultimately, the realization of deferred tax assets is dependent upon generation of future taxable income during those periods in which temporary differences become deductible and/or credits can be utilized. To this end, management considers the level of historical taxable income, the scheduled reversal of deferred tax liabilities, tax-planning strategies and projected future taxable income. Based on these considerations, and the carry-forward availability of a portion of the deferred tax assets, management believes it is more likely than not that we will realize the benefit of the deferred tax assets. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act ("CARES" Act) was enacted and signed into law in response to the COVID-19 pandemic. The CARES Act, among other things, permits NOL carryovers and carrybacks to offset 100% of taxable income for taxable years beginning after 2017 and before 2021. In addition, the CARES Act allows NOLs generated after 2017 and before 2021 to be carried back to each of the five preceding taxable years to generate a refund of previously paid income taxes or carried forward indefinitely. As a result, we have carried the NOL generated in 2019 back to offset the taxable income in the 2014 tax year generating a refund of $36.6 million. This refund was received at the end of the second quarter. We have also amended our 2018 tax return to generate an NOL by electing bonus depreciation. We then carried the NOL generated in 2018 back to offset the taxable income in prior years generating a refund of $26.3 million, of which $4.9 million was received during the fourth quarter. The remaining $21.4 million of this refund has been reclassified from deferred tax asset to accounts receivable in our balance sheets as of December 31, 2020. The deferred tax assets related to the NOLs generated in 2018 and 2019 were recorded at the statutory income tax rate for 2018 and 2019, which was 21% for both years. As a result of the carry back of these NOLs to prior years, the NOLs will be utilized at the statutory income tax rate for pre-2018, which was 35%. This increase in the tax rate at which the 2018 and 2019 NOLs will be utilized results in a deferred tax benefit. Accordingly, as of the year ended December 31, 2020, we recorded a deferred tax benefit of $22.3 million. We are currently still evaluating all provisions of the CARES Act and its impact on income taxes and our Consolidated Statements of Operation. Income tax benefit (in thousands) consisted of the following for the years ended December 31, 2020, 2019 and 2018: Year ended December 31, 2020 2019 2018 Current: Federal $ — $ — $ 1,076 State (307) (1,188) (2,496) Foreign (1,473) (1,343) (518) (1,780) (2,531) (1,938) Deferred: Federal 57,214 90,457 25,578 State 4,591 11,225 5,492 Foreign — — — 61,805 101,682 31,070 Income tax benefit $ 60,025 $ 99,151 $ 29,132 Income tax benefit (in thousands) differed from the amount that would be provided by applying the U.S. federal statutory rate for the years ended December 31, 2020, 2019 and 2018 due to the following: Year ended December 31, 2020 2019 2018 Income tax (expense) benefit computed at U.S. federal statutory rate $ 36,781 $ 90,070 $ 48,290 Decrease (increase) resulting from: Statutory depletion 1,230 4,679 12,090 Goodwill impairment — — (29,157) Prior year tax return reconciliation (2,084) 3,121 530 State income taxes, net of federal benefit 5,013 9,486 2,592 Adjustment to deferred taxes from the CARES Act 22,318 — — Equity compensation (1,477) (6,440) (653) Other, net (1,756) (1,765) (4,560) Income tax benefit $ 60,025 $ 99,151 $ 29,132 Generally, the largest permanent item in computing both our effective tax rate and taxable income is the deduction allowed for statutory depletion. The deduction for statutory depletion does not necessarily change proportionately to changes in income before income taxes. However, for the year ended 2020, we recorded a permanent tax benefit related to the CARES Act, which represents the largest permanent item in computing our effective tax rate for 2020. Additionally, for the year ended December 31, 2018, the tax effect of the goodwill impairment described in Note Y - Impairments is a significant permanent item in the effective tax rate calculation. Deferred tax assets and liabilities are recognized for the estimated future tax effects, based on enacted tax laws, of temporary differences between the values of assets and liabilities recorded for financial reporting and for tax purposes and of net operating loss and other carryforwards. The tax effects of the types of temporary differences and carry forwards that gave rise to deferred tax assets and liabilities (in thousands) at December 31, 2020 and 2019 consisted of the following: December 31, 2020 2019 Gross deferred tax assets: Net operating loss carry forward and state tax credits $ 90,087 $ 32,173 Pension and post-retirement benefit costs 11,146 13,976 Alternative minimum tax credit carry forward — 7,895 Property, plant and equipment 6,866 7,179 Accrued expenses 12,397 15,336 Inventories 121 6,507 Federal tax credits 4,188 — Stock-based compensation expense 4,307 2,390 Interest expense limitation 14,127 22,324 Intangibles 11,304 — Lease obligation liability 14,154 29,604 Other 5,286 5,536 Total deferred tax assets 173,983 142,920 Gross deferred tax liabilities: Land and mineral property basis difference (122,265) (124,182) Fixed assets and depreciation (100,640) (44,314) Intangibles — (12,541) Other (464) (468) Total deferred tax liabilities (223,369) (181,505) Net deferred tax liabilities $ (49,386) $ (38,585) We have federal net operating loss carry forwards of approximately $377.1 million at December 31, 2020. A portion of those losses are subject to an annual limitation under Internal Revenue Code Section 382, but are expected to be fully realized. NOL deductions generated in tax years after December 31, 2017 can offset 100% of taxable income for periods prior to 2021 but only 80% of taxable income after 2020. The CARES Act also prohibits NOL carrybacks on NOLs generated after December 31, 2020 but allows indefinite carryforwards. As of December 31, 2020, we have general business credits of approximately $4.2 million, which will expire beginning in 2033. These credits are expected to be fully realized. As of the years ended December 31, 2020 and 2019, we have an alternative minimum tax credit carry forward of approximately $16.0 million and $16.2 million, respectively. The CARES Act also accelerates the ability of companies to receive refunds of alternative minimum tax ("AMT") credits related to tax years beginning in 2018 and 2019. AMT credits have been presented as a receivable or a deferred tax asset in the prior period balance sheets. The presentation of refundable AMT credits in the current balance sheet has been reclassified from deferred tax asset to accounts receivable to reflect the timing of when the credits are expected to be monetized. AMT credits in the amount of $16.0 million are included in accounts receivable on our balance sheets as of December 31, 2020. See Note F - Accounts Receivable. Additionally, the CARES Act provides temporary relief for payment of certain payroll taxes. Prior to the CARES Act, payroll taxes generally would have been deductible for income tax purposes in the same period that they were expensed for book purposes under the "recurring item exception" of the Internal Revenue Code. However, if a company defers payment of its payroll taxes as a result of the CARES Act such that the recurring item exception no longer applies, accrued payroll taxes would not be deductible until the tax year in which they are actually paid. If the book expense and tax deduction are expected to occur in different periods, a deferred tax asset would need to be recorded for the deductible temporary difference related to the payroll tax accrual. As of December 31, 2020, our net deferred tax liability balance included deferred tax assets of $1.2 million related to deferred payroll taxes. At the end of each reporting period as presented, there were no material amounts of interest and penalties recognized in the statement of operations or balance sheets. We have no material unrecognized tax benefits or any known material tax contingencies at December 31, 2020 or December 31, 2019 and do not expect this to change significantly within the next twelve months. Tax returns filed with the IRS for the years 2017 through 2019 along with tax returns filed with numerous state entities remain subject to examination.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
REVENUE	NOTE T— REVENUE We consider sales disaggregated at the product and service level by business segment to depict how the nature, amount, timing and uncertainty of revenues and cash flow are impacted by changes in economic factors. The following table reflects our sales disaggregated by major source for the years ended December 31, 2020 and 2019 (in thousands): Year Ended December 31, 2020 Year Ended December 31, 2019 Category Oil & Gas Proppants Industrial & Specialty Products Total Sales Oil & Gas Proppants Industrial & Specialty Products Total Sales Product $ 301,199 $ 430,988 $ 732,187 $ 704,516 $ 463,956 $ 1,168,472 Service 113,698 — 113,698 306,005 — 306,005 Total Sales $ 414,897 $ 430,988 $ 845,885 $ 1,010,521 $ 463,956 $ 1,474,477 The following tables reflect the changes in our contract assets, which we classify as unbilled receivables and our contract liabilities, which we classify as deferred revenues, for the years ended December 31, 2020 and 2019 (in thousands): Unbilled Receivables December 31, 2020 December 31, 2019 Beginning Balance $ 20,144 $ 90 Reclassifications to billed receivables (10,330) (3,983) Revenues recognized in excess of period billings 38,168 24,037 Ending Balance $ 47,982 $ 20,144 We enter into certain customer supply agreements which give the customers the right to purchase certain products for a discounted price at certain volumes over an average initial contract term of one Deferred Revenue December 31, 2020 December 31, 2019 Beginning Balance $ 50,634 $ 113,319 Revenues recognized from balances held at the beginning of the period (19,704) (65,225) Revenues deferred from period collections on unfulfilled performance obligations 6,627 12,225 Revenues recognized from period collections (3,865) (9,685) Ending Balance $ 33,692 $ 50,634 We have elected to use the practical expedients allowed under ASC 606-10-50-14, pursuant to which we have excluded disclosures of transaction prices allocated to remaining performance obligations and when we expect to recognize such revenue. The majority of our remaining performance obligations are primarily comprised of unfulfilled product, transportation service, and labor service orders, all of which hold a remaining duration of less than one year. The long term portion of deferred revenue primarily represents a combination of refundable and nonrefundable customer prepayments for which related current performance obligations do not yet exist, but are expected to arise, before the expiration of the contract. Our residual unfulfilled performance obligations are comprised primarily of long-term equipment rental arrangements in which we recognize revenues equal to what we have a right to invoice. Generally, no variable consideration exists related to our remaining performance obligations and no consideration is excluded from the associated transaction prices. However, the decrease in the current year deferred revenue balance is partially attributable to revenue recognized as variable consideration from shortfall penalties assessed to multiple customers according to contract terms as of December 31, 2020 and 2019. For the years ended December 31, 2020 and 2019, we recognized revenue as variable consideration from shortfall penalties according to contract terms in the amounts of $48.0 million and $70.6 million, respectively. In some cases, amounts recorded are estimates which are in negotiation and may increase or decrease. We believe these amounts are the best estimates of revenue to recognize as of year end. Foreign Operations The following table includes information related to our foreign operations for the years ended December 31, 2020, 2019, and 2018 (in thousands): December 31, 2020 December 31, 2019 December 31, 2018 Total Sales $ 86,179 $ 92,788 $ 66,917 Pre-tax income $ 8,509 $ 7,010 $ 5,901 Net income $ 6,722 $ 5,538 $ 4,662 Foreign operations constituted approximately $31.0 million and $27.7 million of consolidated assets as of December 31, 2020 and 2019, respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	NOTE U— RELATED PARTY TRANSACTIONS A former employee, who was an officer of one of our operating subsidiaries prior to the third quarter of 2018, held an ownership interest in a transportation brokerage and logistics services vendor, from which we made purchases of approximately $2.9 million for the year ended December 31, 2018. There were no related party transactions during the years ended December 31, 2020 or 2019.

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
SEGMENT REPORTING	NOTE V— 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. In the Oil & Gas Proppants segment, we serve the oil and gas recovery market primarily by providing and delivering 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 400 product types and materials used in a variety of markets including building and construction products, fillers and extenders, filtration, glassmaking, absorbents, foundry, and sports and recreation. An operating segment’s performance is primarily evaluated based on segment contribution margin, which excludes selling, general, and administrative costs, corporate costs, plant capacity expansion expenses, and facility closure costs. We believe that segment contribution margin, as defined above, is an appropriate measure for evaluating the operating performance of our segments. However, segment contribution margin is a non-GAAP measure and should be considered in addition to, not a substitute for, or superior to, net income (loss) or other measures of financial performance prepared in accordance with GAAP. The other accounting policies of each of the two reportable segments are the same as those in Note B - Summary of Significant Accounting Policies to these Consolidated Financial Statements. The following table presents sales and segment contribution margin (in thousands) for the reportable segments and other operating results not allocated to the reported segments for the years ended December 31, 2020, 2019 and 2018: Year Ended 2020 2019 2018 Sales: Oil & Gas Proppants $ 414,897 $ 1,010,521 $ 1,182,991 Industrial & Specialty Products 430,988 463,956 394,307 Total sales 845,885 1,474,477 1,577,298 Segment contribution margin: Oil & Gas Proppants 142,041 248,594 357,846 Industrial & Specialty Products 159,176 178,215 155,084 Total segment contribution margin 301,217 426,809 512,930 Operating activities excluded from segment cost of sales (1) (30,402) (85,625) (98,761) Selling, general and administrative (124,171) (150,848) (146,971) Depreciation, depletion and amortization (155,568) (179,444) (148,832) Goodwill and other asset impairments (110,688) (363,847) (281,899) Interest expense (79,885) (95,472) (70,564) Other income (expense), net, including interest income 24,350 19,519 4,144 Income tax benefit 60,025 99,151 29,132 Net loss $ (115,122) $ (329,757) $ (200,821) Less: Net loss attributable to non-controlling interest (1,028) (675) (13) Net loss attributable to U.S. Silica Holdings, Inc. $ (114,094) $ (329,082) $ (200,808) (1) 2019 and 2018 mainly driven by plant capacity expansion expenses, amortization of purchase accounting inventory fair value step-up, and facility closure costs. 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. At December 31, 2020, goodwill of $185.6 million has been allocated to these segments with zero assigned to Oil & Gas Proppants and $185.6 million to Industrial & Specialty Products. At December 31, 2019, goodwill of $273.5 million had been allocated to these segments with $86.1 million assigned to Oil & Gas Proppants and $187.4 million to Industrial & Specialty Products.

Unaudited Supplementary Data

Unaudited Supplementary Data	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
UNAUDITED SUPPLEMENTARY DATA	NOTE W— UNAUDITED SUPPLEMENTARY DATA The following table sets forth our unaudited quarterly consolidated statements of operations (in thousands, except per share data) for each of the four quarters in the years ended December 31, 2020 and 2019. This unaudited quarterly information has been prepared on the same basis as our annual audited financial statements and includes all adjustments, consisting only of normal recurring adjustments that are necessary to present fairly the financial information for the fiscal quarters presented. First Second Third Fourth 2020 (Unaudited) Sales: Product $ 222,161 $ 160,200 $ 159,637 $ 190,189 Service 47,438 12,337 16,835 37,088 Cost of sales (excluding depreciation, depletion and amortization): Product 165,496 114,130 93,747 113,609 Service 35,821 10,613 13,845 27,809 Operating expenses: Selling, general and administrative 30,052 39,126 27,216 27,777 Depreciation, depletion and amortization 38,449 37,086 40,069 39,964 Goodwill and other asset impairments 103,866 3,956 222 2,644 Total operating expenses 172,367 80,168 67,507 70,385 Operating (loss) income (104,085) (32,374) 1,373 15,474 Other (expense) income: Interest expense (22,277) (22,179) (19,274) (16,155) Other income (expense), net, including interest income 17,671 (1,670) (409) 8,758 Total other expense (4,606) (23,849) (19,683) (7,397) (Loss) income before income taxes (108,691) (56,223) (18,310) 8,077 Income tax benefit (expense) 36,086 23,605 4,094 (3,760) Net (loss) income (72,605) (32,618) (14,216) 4,317 Less: Net loss attributable to non-controlling interest (260) (264) (254) (250) Net (loss) income attributable to U.S. Silica Holdings, Inc. $ (72,345) $ (32,354) $ (13,962) $ 4,567 (Loss) earnings per share, basic $ (0.98) $ (0.44) $ (0.19) $ 0.06 (Loss) earnings per share, diluted $ (0.98) $ (0.44) $ (0.19) $ 0.06 Weighted average shares outstanding, basic 73,467 73,620 73,688 73,728 Weighted average shares outstanding, diluted 73,467 73,620 73,688 74,328 Dividends declared per share $ 0.02 $ — $ — $ — First Second Third Fourth 2019 (Unaudited) Sales: Product $ 296,860 $ 303,041 $ 287,977 $ 280,594 Service 81,890 91,813 73,837 58,465 Cost of sales (excluding depreciation, depletion and amortization): Product 234,916 225,473 226,797 212,905 Service 62,622 68,687 56,836 45,057 Operating expenses: Selling, general and administrative 34,656 38,659 40,208 37,325 Depreciation, depletion and amortization 44,600 44,899 47,126 42,819 Goodwill and other asset impairments — — 130 363,717 Total operating expenses 79,256 83,558 87,464 443,861 Operating income (loss) 1,956 17,136 (9,283) (362,764) Other (expense) income: Interest expense (23,978) (23,765) (24,733) (22,996) Other income, net, including interest income 722 15,074 3,280 443 Total other expense (23,256) (8,691) (21,453) (22,553) (Loss) income before income taxes (21,300) 8,445 (30,736) (385,317) Income tax benefit (expense) 1,972 (2,384) 7,671 91,892 Net (loss) income (19,328) 6,061 (23,065) (293,425) Less: Net loss attributable to non-controlling interest (4) (89) (28) (554) Net (loss) income attributable to U.S. Silica Holdings, Inc. $ (19,324) $ 6,150 $ (23,037) $ (292,871) (Loss) earnings per share, basic $ (0.26) $ 0.08 $ (0.31) $ (4.00) (Loss) earnings per share, diluted $ (0.26) $ 0.08 $ (0.31) $ (4.00) Weighted average shares, basic 73,040 73,301 73,328 73,343 Weighted average shares, diluted 73,040 73,505 73,328 73,343 Dividends declared per share $ 0.06 $ 0.06 $ 0.06 $ 0.06

Parent Company Financials

Parent Company Financials	12 Months Ended
	Dec. 31, 2020
Condensed Financial Information Disclosure [Abstract]
PARENT COMPANY FINANCIALS	NOTE X— PARENT COMPANY FINANCIALS U.S. SILICA HOLDINGS, INC. (PARENT COMPANY ONLY) CONDENSED BALANCE SHEETS December 31, 2020 2019 (in thousands) ASSETS Current Assets: Cash and cash equivalents $ 46,851 $ 51,849 Due from affiliates 168,276 138,988 Total current assets 215,127 190,837 Investment in subsidiaries 412,169 530,830 Total assets $ 627,296 $ 721,667 LIABILITIES AND STOCKHOLDERS’ EQUITY Current Liabilities: Accrued expenses and other current liabilities $ 286 $ 129 Dividends payable 219 4,958 Total current liabilities 505 5,087 Total liabilities 505 5,087 Stockholders’ Equity: Preferred stock — — Common stock 827 823 Additional paid-in capital 1,200,023 1,185,116 Retained deficit (395,496) (279,956) Treasury stock, at cost (181,615) (180,912) Accumulated other comprehensive loss (8,479) (19,854) Total U.S. Silica Holdings, Inc. stockholders’ equity 615,260 705,217 Non-controlling interest 11,531 11,363 Total stockholders' equity 626,791 716,580 Total liabilities and stockholders’ equity $ 627,296 $ 721,667 U.S. SILICA HOLDINGS, INC. (PARENT COMPANY ONLY) CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) Year ended December 31, 2020 2019 2018 (in thousands) Sales $ — $ — $ — Cost of sales — — — Operating expenses Selling, general and administrative 253 253 254 Total operating expenses 253 253 254 Operating loss (253) (253) (254) Other income (expense) Interest income 210 1,440 2,784 Total other income 210 1,440 2,784 (Loss) income before income taxes and equity in net earnings of subsidiaries (43) 1,187 2,530 Income tax expense — (327) (696) (Loss) income before equity in net earnings of subsidiaries (43) 860 1,834 Equity in earnings of subsidiaries, net of tax (115,079) (330,617) (202,655) Net loss (115,122) (329,757) (200,821) Less: Net loss attributable to non-controlling interest (1,028) (675) (13) Net loss attributable to U.S. Silica Holdings, Inc. (114,094) (329,082) (200,808) Net loss (115,122) (329,757) (200,821) Other comprehensive (loss) income Unrealized loss on derivatives (net of tax of $973, $(456), and $(470) for 2020, 2019, and 2018, respectively) 3,053 (1,432) (1,545) Foreign currency translation adjustment (net of tax of $444, $(60), and $(196) for 2020, 2019 and 2018, respectively) 1,391 (188) (614) Pension and other post-retirement benefits liability adjustment (net of tax of $2,207, $(1,024), and $339 for 2020, 2019 and 2018, respectively) 6,931 (3,214) 1,065 Comprehensive loss (103,747) (334,591) (201,915) Less: Comprehensive loss attributable to non-controlling interest (1,028) (675) (13) Comprehensive loss attributable to U.S. Silica Holdings, Inc. (102,719) (333,916) (201,902) U.S. SILICA HOLDINGS, INC. (PARENT COMPANY ONLY) CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY (amounts in thousands) Par Value Treasury Stock Additional Paid-In Capital Retained Earnings - Present Accumulated Other Comprehensive Income (Loss) Total U.S. Silica, Inc. Stockholders' Equity Non-controlling Interest Total Balance at January 1, 2018 $ 812 $ (25,456) $ 1,147,084 $ 287,992 $ (13,926) $ 1,396,506 $ — $ 1,396,506 Net loss — — — (200,808) — (200,808) (13) (200,821) Unrealized loss on derivatives — — — — (1,545) (1,545) — (1,545) Foreign currency translation adjustment — — — — (614) (614) — (614) Pension and post-retirement liability — — — — 1,065 1,065 — 1,065 Cash dividend declared ($0.25 per share) — — — (19,330) — (19,330) — (19,330) Common stock-based compensation plans activity: Equity-based compensation — — 22,337 — — 22,337 — 22,337 Proceeds from options exercised — 93 (32) — — 61 — 61 Shares withheld for employee taxes related to vested restricted stock and stock units 6 (4,383) (6) — — (4,383) — (4,383) Repurchase of common stock (148,469) (148,469) — (148,469) Balance at December 31, 2018 $ 818 $ (178,215) $ 1,169,383 $ 67,854 $ (15,020) $ 1,044,820 $ 7,484 $ 1,052,304 Net loss — — — (329,082) — (329,082) (675) (329,757) Unrealized loss on derivatives — — — — (1,432) (1,432) — (1,432) Foreign currency translation adjustment — — — — (188) (188) — (188) Pension and post-retirement liability — — — — (3,214) (3,214) — (3,214) Cash dividend declared ($0.25 per share) — — — (18,728) — (18,728) — (18,728) Contributions from non-controlling interest — — — — — — 4,554 4,554 Common stock-based compensation plans activity: Equity-based compensation — — 15,906 — — 15,906 — 15,906 Proceeds from options exercised — 296 (168) — — 128 — 128 Shares withheld for employee taxes related to vested restricted stock and stock units 5 (2,993) (5) — — (2,993) — (2,993) Balance at December 31, 2019 $ 823 $ (180,912) $ 1,185,116 $ (279,956) $ (19,854) $ 705,217 $ 11,363 $ 716,580 Net loss — — — (114,094) — (114,094) (1,028) (115,122) Unrealized gain on derivatives — — — — 3,053 3,053 — 3,053 Foreign currency translation adjustment — — — — 1,391 1,391 — 1,391 Pension and post-retirement liability — — — — 6,931 6,931 — 6,931 Cash dividend declared ($0.02 per share) — — — (1,446) — (1,446) — (1,446) Contributions from non-controlling interest — — — — — — 1,196 1,196 Common stock-based compensation plans activity: Equity-based compensation — — 14,911 — — 14,911 — 14,911 Shares withheld for employee taxes related to vested restricted stock and stock units 4 (703) (4) — — (703) — (703) Balance at December 31, 2020 $ 827 $ (181,615) $ 1,200,023 $ (395,496) $ (8,479) $ 615,260 $ 11,531 $ 626,791 U.S. SILICA HOLDINGS, INC. (PARENT COMPANY ONLY) CONDENSED STATEMENTS OF CASH FLOWS Year ended December 31, 2020 2019 2018 (in thousands) Operating activities: Net loss $ (115,122) $ (329,757) $ (200,821) Adjustments to reconcile net (loss) income to net cash provided by operating activities: Undistributed loss (income) from equity method investment, net 115,079 330,617 202,655 Changes in assets and liabilities, net of effects of acquisitions: Accounts payable and accrued liabilities 155 (88) (295) Net cash provided by operating activities 112 772 1,539 Investing activities: Investment in subsidiary — — — Net cash used in investing activities — — — Financing activities: Dividends paid (6,185) (18,592) (19,912) Repurchase of common stock — — (148,469) Proceeds from options exercised — 128 61 Tax payments related to shares withheld for vested restricted stock and stock units (703) (2,993) (4,383) Contributions from non-controlling interest 1,196 4,554 7,497 Net financing activities with subsidiaries 582 (39,171) 40,171 Net cash used in financing activities (5,110) (56,074) (125,035) Net decrease in cash and cash equivalents (4,998) (55,302) (123,496) Cash and cash equivalents, beginning of period 51,849 107,151 230,647 Cash and cash equivalents, end of period $ 46,851 $ 51,849 $ 107,151 Supplemental cash flow information: Cash (received) paid during the period for: Interest $ (210) $ (1,440) $ (2,784) Notes to Condensed Financial Statements of Registrant (Parent Company Only) These condensed parent company only financial statements have been prepared in accordance with Rule 12-04, Schedule I of Regulation S-X, because the restricted net assets of the subsidiaries of U.S. Silica Holdings, Inc. (as defined in Rule 4-08(e)(3) of Regulation S-X) exceed 25% of the consolidated net assets of the Company. The ability of the Company's operating subsidiaries to pay dividends may be restricted due to the terms of the Company's Credit Facility, as discussed in Note K - Debt to these financial statements. These condensed parent company financial statements have been prepared using the same accounting principles and policies described in the notes to the consolidated financial statements; the only exceptions are that (a) the parent company accounts for its subsidiaries using the equity method of accounting, (b) taxes are allocated to the parent from the subsidiary using the separate return method, and (c) intercompany loans are not eliminated. In the parent company financial statements, the Company's investment in subsidiaries is stated at cost plus equity in undistributed earnings of subsidiaries since the date of acquisition. These condensed parent company financial statements should be read in conjunction with the Company's consolidated financial statements and related notes thereto included elsewhere in this report.

Impairments

Impairments	12 Months Ended
	Dec. 31, 2020
Disclosure Text Block Supplement [Abstract]
IMPAIRMENTS	NOTE Y— IMPAIRMENTS We recorded impairment charges (in thousands) for the years ended December 31, 2020, 2019 and 2018 for the following assets: Description December 31, 2020 December 31, 2019 December 31, 2018 Inventories, net $ 6,837 $ 4,100 $ 3,316 Property, plant and mine development, net 11,822 243,064 109,938 Operating lease right-of-use assets 3,406 115,443 — Goodwill 86,100 — 164,167 Intangible assets, net 2,523 1,240 4,478 Total $ 110,688 $ 363,847 $ 281,899 2020 Impairments During 2020, there was an unprecedented drop in global demand combined with the breakdown of the Organization of the Petroleum Exporting Countries and other oil producing nations ("OPEC+") agreement to restrict oil production that led to one of the largest annual crude oil inventory builds in history. This led to a sharp reduction in global crude oil prices. Containment measures and other economic, travel, and business disruptions caused by COVID-19 also affected refinery activity and future demand for crude oil, and consequently, the services and products of our Oil & Gas Proppants segment. As a result of these triggering events, we completed impairment assessments for our assets, including plant, property and mine development, right-of-use assets, inventories, and other intangible assets. Inventories, net We recorded impairment charges primarily related to unused inventory at plants we idled. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. Property, plant and mine development We estimated the future undiscounted net cash flows of certain asset groupings using estimates of proven and probable sand reserves, estimated future sales prices (considering historical and current prices, price trends and related factors) and operating costs and anticipated capital expenditures. In the cases where the undiscounted cash flows are less than the carrying value of the assets, we recognized an impairment loss equal to the amount by which the carrying value exceeds the fair value of the assets. Impairment charges were recorded related primarily to our Kosse, Texas facility, which was idled. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. Operating lease right-of-use assets We determined the fair value of the railcars primarily utilizing internally developed cash flow models and quoted market prices, discounted at an appropriate weighted average cost of capital. As a result, we recognized impairment charges primarily related to various equipment leases and an office building lease. These charges relate mainly to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. Goodwill We performed a quantitative analysis and determined that the goodwill of our Oil & Gas Proppants reporting unit was impaired. We recognized goodwill impairment charges during the first quarter of 2020. These impairment charges were recorded in the "Goodwill and other asset impairments" caption of our Consolidated Statements of Operations. The fair value of our reporting units was determined using the discounted cash flow method. Intangible assets, net We recorded impairments of $1.1 million for trade names and $1.4 million for patents and intellectual property as of December 31, 2020, which was recorded in the Industrial & Specialty Products segment as a result of the discontinuance of a minor product line. These charges were recorded in the "Goodwill and other asset impairments" caption of our Consolidated Statements of Operations. 2019 Impairments During the fourth quarter of 2019, similar to the fourth quarter of 2018, we experienced a sharp decline in customer demand for Northern White frac sand and for regional non-in-basin frac sand as more tons are produced and sold in-basin. Additionally, the price of frac sand decreased significantly. Given the changes in demand and customer preferences of local in-basin sand, we also experienced a significant decline in the utilization of the sand railcar fleet in our transload network. A significant number of sand railcars were put into storage and were no longer used to deliver sand to our customers. In response to these economic conditions, we implemented numerous cost reductions including headcount reductions and a reduction of frac sand capacity at multiple locations. As a result of the aforementioned triggering events, which occurred in the fourth quarter of 2019, we completed an impairment assessment of our frac sand-related assets, including plant, property and mine development, right-of-use assets, inventories, and other intangible assets. Inventories, net We recorded impairment charges for unused inventory at frac sand plants we idled. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. Property, plant and mine development We estimated the future undiscounted net cash flows of asset groupings, which are at the plant level, using estimates of proven and probable sand reserves, estimated future sales prices (considering historical and current prices, price trends and related factors) and operating costs and anticipated capital expenditures. In the cases where the undiscounted cash flows are less than the carrying value of the assets, we recognized an impairment loss equal to the amount by which the carrying value exceeds the fair value of the assets. Impairment charges were recorded mainly related to facilities that have reduced capacity or have been idled, including Tyler, Texas, Sparta, Wisconsin, and Utica, Illinois. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. Operating lease right-of-use assets We determined the fair value of the railcars primarily utilizing internally developed cash flow models and quoted market prices, discounted at an appropriate weighted average cost of capital. As a result, we recognized impairment charges to write down the value of railcars to their estimated fair value. These charges relate mainly to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. Intangible assets, net We recorded an impairment of customer relationships related to the Oil & Gas Proppants segment that was recorded in the "Goodwill and other asset impairments" caption of our Consolidated Statements of Operations. 2018 Impairments During the fourth quarter of 2018, we experienced a declining shift in demand for Northern White sand caused by some of our customers shifting to local in-basin frac sands with lower logistics costs. Our largest customer at our Voca, Texas plant did not renew their contract, instead opting to sign a new contract with us for local in-basin frac sand. Additionally, Northern White Sand operations and reserves in Fairchild, Wisconsin and Peru, Illinois experienced a similar significant fourth quarter decline in demand due to customers' shift to local in-basin sand closer to their operations. As a result of these triggering events, we completed an impairment assessment of our frac sand-related assets, including plant, property and mine development, goodwill and other intangible assets. Inventories, net We recorded impairment charges for unused inventory related to the closure of our resin coating facility and associated product portfolio. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. Property, plant and mine development We estimated the future undiscounted net cash flows of asset groupings using estimates of proven and probable sand reserves, estimated future sales prices (considering historical and current prices, price trends and related factors) and operating costs and anticipated capital expenditures. In the cases where the undiscounted cash flows are less than the carrying value of the assets, we recognized an impairment loss equal to the amount by which the carrying value exceeds the fair value of the assets. Impairment charges were recorded mainly related to facilities that have reduced capacity, have been idled or were undeveloped, including Voca, Texas, Fairchild, Wisconsin, Rochelle, Illinois, and Peru, Illinois. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. Goodwill and Intangible Assets, net

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS We evaluated subsequent events through the date the consolidated financial statements were available for issuance and did not identify any events requiring disclosure.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying Consolidated Financial Statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). In the opinion of management, all adjustments necessary for a fair presentation of the Consolidated Financial Statements have been included. Such adjustments are of a normal, recurring nature. Throughout this report we refer to (i) our Consolidated Balance Sheets as our “Balance Sheets,” (ii) our Consolidated Statements of Operations as our “Income Statements,” and (iii) our Consolidated Statements of Cash Flows as our “Cash Flows.”
Consolidation	Consolidation The Consolidated Financial Statements include the accounts of Holdings and its direct and indirect wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. We follow FASB Accounting Standards Codification (“ASC”) guidance for identification and reporting of entities over which control is achieved through means other than voting rights. The guidance defines such entities as Variable Interest Entities (“VIEs”). We consolidate VIEs when we have variable interests and are the primary beneficiary. We continually evaluate our involvement with VIEs to determine when these criteria are met.
Reclassifications	Reclassifications Certain reclassifications of prior period presentations have been made to conform to the current period presentation.
Use of Estimates and Assumptions	Use of Estimates and Assumptions The preparation of Consolidated Financial Statements in conformity with GAAP requires management 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 Consolidated Financial Statements and the reported amounts of revenues and expenses during the reporting period. The areas requiring the use of management estimates and assumptions relate to the purchase price allocation for businesses acquired; 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 provision for credit losses; estimates of fair value for certain reporting units and asset impairments (including impairments of goodwill, intangible assets 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; contingent considerations; 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.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of all highly liquid investments with a maturity of three months or less when purchased. Because of the short maturity of these investments, the carrying amounts approximate their fair value. Cash and cash equivalents are invested primarily in money market securities held by financial institutions with high credit ratings. Accounts at each institution are insured by the Federal Deposit Insurance Corporation. Cash balances at times may exceed federally-insured limits. We have not experienced any losses in such accounts and believe we are not exposed to any significant credit risk on cash.
Accounts Receivables	Accounts ReceivableThe majority of our accounts receivable are due from companies in the oil and natural gas drilling, building and construction products, filler and extenders, filtration, glass, absorbents, sports and recreation, foundry and other major industries. Credit is extended based on evaluation of a customer’s financial condition and, generally, collateral is not required. Accounts receivable are stated at amounts due from customers net of provision for credit losses. Accounts outstanding longer than the payment terms are considered past due. We determine our allowance by considering a number of factors, including the length of time trade accounts receivable are past due, our previous loss history, the customer’s current ability to pay its obligation to us and the condition of the general economy and the industry as a whole. Ongoing credit evaluations are performed. We write-off accounts receivable when they are deemed uncollectible, and payments subsequently received on such receivables are credited to the provision for credit losses.
Inventories	InventoriesInventories include raw stockpiles, in-process product and finished product available for shipment, as well as spare parts and supplies for routine facility maintenance. We value inventory at the lower of cost and net realizable value. Cost is determined using the first-in, first-out and average cost methods. Our inventoriable costs include production costs and transportation and additional service costs as applicable.
Property, Plant and Mine Development	Property, Plant and Mine Development Plant and equipment Plant and equipment is recorded at cost and depreciated over their estimated useful lives. Interest incurred during construction of facilities is capitalized and depreciated over the life of the asset. Costs for normal repairs and maintenance that do not extend economic life or improve service potential are expensed as incurred. Costs of improvements that extend economic life or improve service potential are capitalized and depreciated over the estimated remaining useful life. Depreciation is recorded using the straight-line method over the assets’ estimated useful lives as follows: buildings (15 years); land improvements (10 years); machinery and equipment, including computer equipment and software (3-10 years); furniture and fixtures (8 years). Leasehold improvements are depreciated over the shorter of the asset life or lease term. Construction-in-progress is primarily comprised of machinery and equipment which have not yet been placed in service. Mining property and development Mining property and development includes mineral deposits and mine exploration and development. Mineral deposits are initially recognized at cost, which approximates the estimated fair value on the date of purchase. Mine exploration and development costs include engineering and mineral studies, drilling and other related costs to delineate an ore body, and the removal of overburden to initially expose an ore body for production. Costs incurred before mineralization are classified as proven and probable reserves are expensed and classified as exploration or advanced projects, research and development expense. Capitalization of mine development project costs, which meet the definition of an asset, begins once mineralization is classified as proven and probable reserves. The cost of removing overburden and waste materials to access the ore body at an open pit mine prior to the production phase are referred to as “pre-stripping costs.” Pre-stripping costs are capitalized during the development of an open pit mine. The production phase of an open pit mine commences when saleable minerals, beyond a de minimis amount, are produced. Stripping costs incurred during the production phase of a mine are variable production costs that are included as a component of inventory to be recognized in costs applicable to sales in the same period as the revenue from the sale of inventory. Depletion and amortization of mineral deposits and mine development costs are recorded as the minerals are extracted, based on units of production and engineering estimates of mineable reserves. The impact of revisions to reserve estimates is recognized on a prospective basis. See Note H - Property, Plant and Mine Development. Mine reclamation costs and asset retirement obligations We recognize the fair value of any liability for conditional asset retirement obligations, if sufficient information exists to reasonably estimate the fair value of the liability. These obligations include environmental remediation liabilities when incurred, which is generally upon acquisition, construction or development and/or through the normal operation of the asset. These obligations also generally include the estimated net future costs of dismantling, restoring and reclaiming operating mines and related mine sites in accordance with federal, state, local regulatory and land lease agreement requirements. The liability is accreted over time through periodic charges to earnings. In addition, the asset retirement cost is capitalized as part of the asset’s carrying value and amortized over the life of the related asset. Reclamation costs are periodically adjusted to reflect changes in the estimated present value resulting from the passage of time and revisions to the estimates of either the timing or amount of the reclamation and abandonment costs. The reclamation obligation is based on when spending for an existing environmental disturbance will occur. If the asset retirement obligation is settled for other than the carrying amount of the liability, a gain or loss is recognized on settlement. We review, on an annual basis, unless otherwise deemed necessary, the reclamation obligation at each mine site in accordance with ASC guidance for accounting for reclamation obligations.
Impairment or Disposal of Property, Plant and Mine Development	Impairment or Disposal of Property, Plant and Mine Development We periodically evaluate whether current events or circumstances indicate that the carrying value of our property, plant and equipment assets may not be recoverable. If circumstances indicate that the carrying value may not be recoverable, we estimate future undiscounted net cash flows using estimates of proven and probable sand reserves, estimated future sales prices (considering historical and current prices, price trends and related factors) and operating costs and anticipated capital expenditures. If the undiscounted cash flows are less than the carrying value of the assets we recognize an impairment loss equal to the amount by which the carrying value exceeds the fair value of the assets. The recoverability of the carrying value of our mineral properties is dependent upon the successful development, start-up and commercial production of our mineral deposit and the related processing facilities. Our evaluation of mineral properties for potential impairment primarily includes assessing the existence or availability of required permits and evaluating changes in our mineral reserves, or the underlying estimates and assumptions, including estimated production costs. Assessing the economic feasibility requires certain estimates including the prices of products to be produced and processing recovery rates, as well as operating and capital costs. Gains on the sale of property, plant and mine development are included in income when the assets are disposed of provided there is more than reasonable certainty of the collectability of the sales price and any future activities required to be performed by us relating to the disposal of the assets are complete or insignificant. Upon retirement or disposal of assets, all costs and related accumulated depreciation or amortization are written-off.
Goodwill and Other Intangible Assets and Related Impairment	Goodwill and Other Intangible Assets and Related ImpairmentOur intangible assets consist of goodwill, which is not being amortized, indefinite-lived intangibles, which consist of certain trade names that are not subject to amortization, intellectual property and customer relationships. Intellectual property mainly consists of patents and technology, and it is amortized on a straight-line basis over an average useful life of 15 years. Customer relationships are amortized on a straight-line basis over their useful life of 13 - 20 years. Intangible assets that are amortized are reviewed for impairment annually, or more frequently when indicators of impairment exist.Goodwill represents the excess of the purchase price of business combinations over the fair value of net assets acquired. Goodwill and trade names are reviewed for impairment annually as of October 31, or more frequently when indicators of impairment exist. An impairment exists if the fair value of a reporting unit to which goodwill has been allocated, or the fair value of indefinite-lived intangible assets, is less than their respective carrying values. Prior to conducting a formal impairment test we have an option to assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that is more likely than not (more than 50%) that the fair value of a reporting unit is less than its carrying amount. Such qualitative factors may include the following: macroeconomic conditions; industry and market considerations; cost factors; overall financial performance; and other relevant entity-specific events. If the qualitative assessment determines that an impairment is more likely than not, or if we choose to bypass the qualitative assessment, we perform a quantitative assessment by comparing the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit.
Leases	Leases We lease railroad cars, office space, mining property, mining/processing equipment and transportation and other equipment. Operating leases are included in operating lease right-of-use (“ROU”) assets, current portion of operating lease liabilities, and operating lease liabilities in our consolidated balance sheets. Finance leases are included in property, plant and mine development, current portion of long-term debt, and long-term debt in our consolidated balance sheets. Leases with an initial term of 12 months or less are not recorded on the balance sheet. ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and liabilities are recognized at the commencement date of the lease based on the present value of lease payments over the lease term. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. The ROU assets also include any lease payments made at or before the commencement date of the lease and excludes lease incentives. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term. We have lease agreements with lease and non-lease components, the latter of which are generally accounted for separately. See Note R - Leases.
Revenue Recognition and Deferred Revenues	Revenue Recognition Products We derive our product sales by mining and processing minerals that our customers purchase for various uses. Our product sales are primarily a function of the price per ton and the number of tons sold. We primarily sell our products through individual purchase orders executed under short-term price agreements or at prevailing market rates. The amount invoiced reflects product, transportation and additional handling services as applicable, such as storage, transloading the product from railcars to trucks and last mile logistics to the customer site. We invoice most of our product customers on a per shipment basis, although for some larger customers, we consolidate invoices weekly or monthly. Standard collection terms are net 30 days, although extended terms are offered in competitive situations. We recognize revenue for products and materials at a point in time following the transfer of control of such items to the customer, which typically occurs upon shipment or delivery depending on the terms of the underlying contracts. We account for shipping and handling activities related to product and material sales contracts with customers as costs to fulfill our promise to transfer the associated products pursuant to the accounting policy election allowed under ASC 606-10-25-18b. Accordingly, we record amounts billed for shipping and handling costs as a component of net sales and accrue and classify related costs as a component of cost of sales at the time revenue is recognized. For a limited number of customers, we sell under long-term, minimum purchase supply agreements. These agreements define, among other commitments, the volume of product that our customers must purchase, the volume of product that we must provide and the price that we will charge and that our customers will pay for each product. Prices under these agreements are generally fixed and subject to certain contractual adjustments. Sometimes these agreements may undergo negotiations regarding pricing and volume requirements, which may often occur in volatile market conditions. While these negotiations continue, we may deliver sand at prices or at volumes below the requirements in our existing supply agreements. An executed order specifying the type and quantity of product to be delivered, in combination with the noted agreements, comprise our contracts in these arrangements. Service We derive our service revenues primarily through the provision of transportation, equipment rental, and contract labor services to companies in the oil and gas industry. Transportation services typically consist of transporting customer proppant from storage facilities to proximal well-sites and are contracted through work orders executed under established pricing agreements. The amount invoiced reflects the transportation services rendered. Equipment rental services provide customers with use of either dedicated or nonspecific wellhead proppant delivery equipment solutions for contractual periods defined either through formal lease agreements or executed work orders under established pricing agreements. The amounts invoiced reflect the length of time the equipment set was utilized in the billing period. Contract labor services provide customers with proppant delivery equipment operators through work orders executed under established pricing agreements. The amounts invoiced reflect the amount of time our labor services were utilized in the billing period. We typically invoice our customers on a weekly or monthly basis; however, some customers receive invoices upon well-site operation completion. Standard collection terms are net 30 days, although extended terms are offered in competitive situations. We typically recognize revenue for specific, dedicated equipment set rental arrangements under ASC 842, Leases. For the remaining components of service revenue, we have applied the practical expedient allowed under ASC 606-10-55-18 to recognize transportation revenues in proportion to the amount we have the right to invoice. Contracts with Multiple Performance Obligations From time to time, we may enter into contracts that contain multiple performance obligations, such as work orders containing a combination of product, transportation, equipment rentals, and contract labor services. For these arrangements, we allocate the transaction price to each performance obligation identified in the contract based on relative standalone selling prices, or estimates of such prices, and recognize the related revenue as control of each individual product or service is transferred to the customer, in satisfaction of the corresponding performance obligations. We typically invoice our customers on a weekly or monthly basis; however, some customers receive invoices upon well-site operation completion. Standard collection terms are net 30 days, although extended terms are offered in competitive situations. Taxes Collected from Customers and Remitted to Governmental Authorities. We exclude from our measurement of transaction prices all taxes assessed by governmental authorities that are both (i) imposed on and concurrent with a specific revenue-producing transaction and (ii) collected from customers. Accordingly, such tax amounts are not included as a component of net sales or cost of sales. See Note T - Revenue. Deferred Revenues one
Unbilled Receivables	Unbilled ReceivablesRevenues recognized in advance of invoice issuance create assets referred to as “unbilled receivables.” Any portion of our unbilled receivables for which our right to consideration is conditional on a factor other than the passage of time is considered a contract asset. These assets are presented on a combined basis with accounts receivable and are converted to accounts receivable once billed.
Debt Issuance Costs	Debt Issuance CostsThe Company defers costs directly associated with acquiring third-party financing, primarily loan origination costs and related professional expenses. Debt issuance costs are deferred and amortized using the effective interest rate method over the term of our senior secured Term Loan facility and the straight-line method for our Revolver facility. Debt issuance costs related to long-term debt are reflected as a direct deduction from the carrying amount of the debt.
Employee Benefit Plans	Employee Benefit PlansWe provide a range of benefits to our employees and retired employees, including pensions and post-retirement healthcare and life insurance benefits. We record annual amounts relating to these plans based on calculations specified by generally accepted accounting principles, which include various actuarial assumptions, including discount rates, assumed rates of returns, compensation increases, turnover rates, mortality tables, and healthcare cost trend rates. We review the actuarial assumptions on an annual basis and make modifications to the assumptions based on current rates and trends when it is deemed appropriate to do so. As required by U.S. generally accepted accounting principles, the effect of the modifications is generally recorded or amortized over future periods. We believe that the assumptions utilized in recording our obligations under the plans are reasonable based on advice from our actuaries and information as to assumptions used by other employers.
Environmental Costs	Environmental Costs Environmental costs, other than qualifying capital expenditures, are accrued at the time the exposure becomes known and costs can be reasonably estimated. Costs are accrued based upon management’s estimates of all direct costs, after taking into account expected reimbursement by third parties (primarily the sellers of acquired businesses) and are reviewed by outside consultants. Environmental costs are charged to expense unless a settlement with an indemnifying party has been reached.
Self-Insurance	Self-InsuranceWe are self-insured for various levels of employee health insurance coverage, workers’ compensation and third-party product liability claims alleging occupational disease. We purchase insurance coverage for claim amounts which exceed our self-insured retentions. Depending on the type of insurance, these self-insured retentions range from $0.1 million to $0.5 million per occurrence. Our insurance reserves are accrued based on estimates of the ultimate cost of claims expected to occur during the covered period. These estimates are prepared with the assistance of outside actuaries and consultants. Our actuaries periodically review the volume and amount of claims activity, and based upon their findings, we adjust our insurance reserves accordingly. The ultimate cost of claims for a covered period may differ from our original estimates. The current portion of our self-insurance reserves is included in accrued liabilities and the non-current portion is included in other long-term obligations in our Balance Sheets.
Research and Development Costs	Research and Development Costs We may incur immaterial internal research and development (“R&D”) expenditures, and research and development conducted for others, all of which are expensed as incurred, and included in selling, general and administrative expense. R&D costs may include, but are not limited to, research and administrative salaries, contractor fees, building costs, utilities, administrative expenses, and allocations of corporate costs.
Advertising Costs	Advertising CostsWe recognize advertising expense when incurred as selling, general and administrative expense.
Equity-based Compensation	Equity-based Compensation We grant stock options, restricted stock, restricted stock units and performance share units to certain of our employees and directors under the Amended and Restated U.S. Silica Holdings, Inc. 2011 Incentive Compensation Plan. We recognize the cost of employee services rendered in exchange for awards of equity instruments. Vesting of restricted stock and restricted stock units is based on the individual continuing to render service over a pre-defined vesting schedule, generally three years. Cash dividend equivalents are accrued and paid to the holders of time-based restricted stock units and restricted stock. The fair value of the restricted stock awards is equal to the market price of our stock at date of grant. The restricted award-related compensation expense is recognized on a straight-line basis over the vesting period. We grant performance share units to certain employees in which the number of shares of common stock ultimately received is determined based on achievement of certain performance thresholds over a specified performance period (generally three years) in accordance with the stock award agreement. Cash dividend equivalents are not accrued or paid on performance share units. We recognize expense based on the estimated vesting of our performance share units granted and the grant date market price. The estimated vesting of the performance share units is principally based on the probability of achieving certain financial performance levels during the vesting periods. In the period it becomes probable that the minimum performance criteria specified in the award agreement will be achieved, we recognize expense for the proportionate share of the total fair value of the award related to the vesting period that has already lapsed. The remaining fair value of the award is expensed on a straight-line basis over the remaining vesting period. We grant certain employees performance share units, the vesting of which is based on the Company’s total shareholder return (“TSR”) ranking among a peer group over a three-year period. The number of units that will vest will depend on the percentage ranking of the Company's TSR compared to the TSRs for each of the companies in the peer group over the performance period. For these awards subject to market conditions, a binomial-lattice model (i.e., Monte Carlo simulation model) is used to fair value these awards at grant date. The related compensation expense is recognized, on a straight-line basis, over the vesting period. We grant stock options to certain employees and directors. Stock options vest on a vesting schedule and the related compensation expense is recognized over the vesting period, usually over three
Income Taxes	Income Taxes Deferred taxes are provided on the liability method whereby deferred tax assets are recognized for deductible temporary differences and operating loss and tax credit carry forwards and deferred tax liabilities are recognized for taxable temporary differences. This approach requires recognition of deferred tax liabilities and assets for the expected future tax consequences of events that have been included in the financial statements or tax returns. Under this method, deferred tax liabilities and assets are determined based upon the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the expenses are expected to reverse. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. We recognize a tax benefit associated with an uncertain tax position when, in management’s judgment, it is more likely than not that the position will be sustained upon examination by a taxing authority. For a tax position that meets the more-likely-than-not recognition threshold, we initially and subsequently measure the tax benefit as the largest amount that we judge to have a greater than 50% likelihood of being realized upon ultimate settlement with a taxing authority. The liability associated with unrecognized tax benefits is adjusted periodically due to changing circumstances, such as the progress of tax audits, case law developments and new or emerging legislation. Such adjustments are recognized entirely in the period in which they are identified. The effective tax rate includes the net impact of changes in the liability for unrecognized tax benefits and subsequent adjustments as considered appropriate by management.
Financial Instruments	Financial InstrumentsWe currently use interest rate hedge agreements to manage interest costs and the risk associated with changing interest rates. Amounts to be paid or received under these hedge agreements are accrued as interest rates change and are recognized over the life of the hedge agreements as an adjustment to interest expense. Our policy is to not hold or issue derivative financial instruments for trading or speculative purposes. When entered into, these financial instruments are designated as hedges of underlying exposures, associated with our long-term debt and are monitored to determine if they remain effective hedges. Gains and losses on derivatives designated as cash flow hedges are recorded in other comprehensive income (loss), net of tax, and reclassified to earnings in a manner that matches the timing of the earnings impact of the hedged transactions. The ineffective portion of all hedges, if any, is recognized currently in income.
Foreign Currency Translation	Foreign Currency Translation
Comprehensive Income (Loss)	Comprehensive Income (loss) In addition to net income (loss), comprehensive income (loss) includes all changes in equity during a period, such as adjustments to minimum pension liabilities and the effective portion of changes in fair value of derivative instruments that qualify as cash flow hedges.
Business Combinations	Business CombinationsThe Company accounts for business combinations using the acquisition method of accounting. Under this method, acquired assets, including separately identifiable intangible assets and any assumed liabilities, are recorded at their acquisition date estimated fair value. The excess of purchase price over the fair value amounts assigned to the assets acquired and liabilities assumed represents the goodwill amount resulting from the acquisition. Determining the fair value of assets acquired and liabilities assumed involves the use of significant estimates and assumptions.
New Accounting Pronouncements Recently Adopted and New Accounting Pronouncements Not Yet Adopted	New Accounting Pronouncements Recently Adopted In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The new guidance requires a customer in a cloud computing arrangement (i.e., hosting arrangement) that is a service contract to follow the internal-use software guidance in ASC 350-40 to determine which implementation costs to capitalize as assets or expense as incurred. Capitalized implementation costs related to a hosting arrangement that is a service contract will be amortized over the term of the hosting arrangement, beginning when the module or component of the hosting arrangement is ready for its intended use. This update was effective for calendar-year public business entities in 2020. We adopted the new standard on January 1, 2020. The adoption of this ASU had no significant impact on our Consolidated Statements of Operations. In November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses. The amendments in this ASU clarified issues related to Topic 326. In Issue 1, the amendment in this ASU mitigates transition complexity by requiring that for nonpublic business entities the amendments in ASU 2016-13 are effective for fiscal years after December 15, 2021, including interim periods within those fiscal years. In Issue 2, the amendment clarifies that receivables arising from operating leases are not within the scope of Subtopic 326-20. Impairment of receivables arising from operating leases should be accounted for in accordance with Topic 842, Leases. The ASU was effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We adopted the new standard on January 1, 2020. The adoption of the new standard did not have a significant impact on our Consolidated Financial Statements as our current process for estimating expected credit losses for trade receivables aligned with the expected credit loss model. See Note F - Accounts Receivable. In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20). The new guidance removes certain disclosure requirements for employers which sponsor defined benefit pension or other post-retirement plans, but also adds disclosure requirements for the weighted average interest crediting rates for cash balance plans and other plans with promised crediting rates and an explanation of the reasons for significant gains and losses related to changes in the benefit obligation for the period. The amendments also clarify disclosure requirements for the projected benefit obligation (PBO) and accumulated benefit obligation (ABO) and fair value of plan assets for plans with PBOs and ABOs in excess of plan assets. Entities should apply the amendments on a retrospective basis for all periods presented. The amendments in this update are effective for public entities for fiscal years ending after December 15, 2020. We have modified our disclosures in the current year to reflect this guidance. There was no impact to our Consolidated Statements of Operations due to the adoption of this guidance. New Accounting Pronouncements Not Yet Adopted In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in this Update simplify the accounting for income taxes by removing several exceptions and also simplify the accounting for income taxes by requiring that an entity recognize a franchise tax (or similar tax) that is partially based on income as an income-based tax and account for any incremental amount incurred as a non-income-based tax, requiring that an entity evaluate when a step up in the tax basis of goodwill should be considered part of the business combination in which the book goodwill was originally recognized and when it should be considered a separate transaction, specifying that an entity is not required to allocate the consolidated amount of current and deferred tax expense to a legal entity that is not subject to tax in its separate financial statements (however, an entity may elect to do so on an entity-by-entity basis) for a legal entity that is both not subject to tax and disregarded by the taxing authority, requiring that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date, and making minor codification improvements for income taxes related to employee stock ownership plans and investments in qualified affordable housing projects accounted for using the equity method. For public business entities, the amendments in this update are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. At this time, we do not believe adopting this guidance will have a material impact to our Consolidated Financial Statements.
Fair Value Measurement	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, quoted 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 December 31, 2020 and 2019, approximate their reported carrying values. 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. Changes in the fair value of the royalty note payable utilize Level 3 inputs, such as estimates of future tonnages sold and average sales price. See Note K - Debt for more information on the change in fair value during the year ended December 31, 2020. As a result of the settlement of this royalty note payable in its entirety during the fourth quarter, the outstanding balance as of December 31, 2020 was zero. Derivative Instruments The estimated fair value of our derivative instruments 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.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Earnings Per Share	The following table shows the computation of basic and diluted earnings per share for the years ended December 31, 2020, 2019 and 2018: In thousands, except per share amounts Year ended December 31, 2020 2019 2018 Numerator: Net loss attributable to U.S. Silica Holdings, Inc. $ (114,094) $ (329,082) $ (200,808) Denominator: Weighted average shares outstanding 73,634 73,253 76,453 Diluted effect of stock awards — — — Weighted average shares outstanding assuming dilution 73,634 73,253 76,453 Loss per share attributable to U.S. Silica Holdings, Inc.: Basic loss per share $ (1.55) $ (4.49) $ (2.63) Diluted loss per share $ (1.55) $ (4.49) $ (2.63)
Schedule of Antidilutive Securities Excluded from Computation of Diluted Earnings (Loss) Per Common Share	Certain stock options, restricted stock awards and performance share units were excluded from the computation of diluted earnings per share because their effect would have been anti-dilutive. Such potentially dilutive shares and stock awards (in thousands) excluded from the calculation of diluted earnings (loss) per common share were as follows: Year ended December 31, 2020 2019 2018 Potentially dilutive shares excluded 238 68 443 Stock options excluded 826 711 574 Restricted stock and performance share units awards excluded 3,435 1,298 155

Capital Structure and Accumul_2

Capital Structure and Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Schedule of Declared Quarterly Cash Dividends	During the year ended December 31, 2020, our Board of Directors declared quarterly cash dividends as follows: Dividends per Common Share Declaration Date Record Date Payable Date $ 0.02 February 10, 2020 March 13, 2020 April 3, 2020
Schedule of Changes in Accumulated Other Comprehensive Income (Loss)	The following table presents the changes in accumulated other comprehensive income (loss) by component (in thousands) during the year ended December 31, 2020: For the Year Ended December 31, 2020 Unrealized income (loss) on cash flow hedges Foreign currency translation adjustments Pension and other post-retirement benefits liability Total Beginning Balance $ (3,053) $ (808) $ (15,993) $ (19,854) Other comprehensive income before reclassifications 3,053 1,391 4,537 8,981 Amounts reclassed from accumulated other comprehensive loss — — 2,394 2,394 Ending Balance $ — $ 583 $ (9,062) $ (8,479)

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Schedule of Identifiable Assets Acquired and Liabilities Assumed	The following table sets forth the final allocation of the purchase price to EPMH's identifiable tangible and intangible assets acquired and liabilities assumed, including measurement period adjustments (in thousands): Final allocation of purchase price: Estimate as of December 31, 2018 Measurement Period Adjustments Purchase Price Allocation Accounts receivable, net $ 43,305 $ — $ 43,305 Inventories 86,112 — 86,112 Property, plant and mine development 148,495 (1,937) 146,558 Mineral rights 419,469 (10,580) 408,889 Identifiable intangible assets - finite lived 10,270 (1,500) 8,770 Identifiable intangible assets - indefinite lived 38,050 (1,250) 36,800 Prepaids and deposits 2,072 (245) 1,827 Other assets 7,474 — 7,474 Goodwill 150,628 12,184 162,812 Total assets acquired 905,875 (3,328) 902,547 Accounts payable 13,435 — 13,435 Accrued expenses and other current liabilities 10,304 — 10,304 Deferred tax liabilities 122,811 (3,328) 119,483 Long term obligations 16,076 — 16,076 Total liabilities assumed $ 162,626 $ (3,328) $ 159,298 Net assets acquired $ 743,249 $ — $ 743,249
Schedule of Identifiable Intangible Assets Acquired	The acquired intangible assets and the related estimated useful lives consist of the following: Approximate Fair Value Estimated Useful Life (in thousands) (in years) Technology and intellectual property $ 1,400 15 Customer relationships 7,370 15 Total identifiable intangible assets - finite lived $ 8,770 Trade names $ 36,800 Total identifiable intangible assets - indefinite lived $ 36,800
Schedule of Pro Forma Information	The following unaudited pro forma consolidated financial information reflects the results of operations as if the EPMH acquisition had occurred on January 1, 2017, after giving effect to certain purchase accounting adjustments. Material non-recurring transaction costs attributable to the business combination were $15.2 million. Pro forma net income includes incremental interest expense due to the related debt financing, incremental depreciation and depletion expense related to the fair value adjustment of property, plant and mine development, amortization expense related to identifiable intangible assets, and tax expense related to the combined tax provisions. 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 (in thousands, except per share amounts): For the year ended December 31, 2018 2017 Sales $ 1,659,775 $ 1,454,070 Net (loss) income $ (179,220) $ 116,899 Basic (loss) earnings per share $ (2.34) $ 1.44 Diluted (loss) earnings per share $ (2.34) $ 1.43

Accounts Receivable (Tables)

Accounts Receivable (Tables)	12 Months Ended
	Dec. 31, 2020
Receivables [Abstract]
Schedule of Accounts Receivable and Allowance for Doubtful Accounts	At December 31, 2020 and December 31, 2019, accounts receivable (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Trade receivables $ 171,230 $ 178,182 Less: Provision for credit losses (6,604) (8,984) Net trade receivables 164,626 169,198 Other receivables (1) 42,308 13,040 Total accounts receivable $ 206,934 $ 182,238 (1) At December 31, 2020, other receivables included $37.4 million of refunds related to NOL carryback claims filed for various tax years in accordance with certain provisions of the CARES Act. At December 31, 2019, other receivables included $8.1 million of refundable alternative minimum tax credits. We classify our trade receivables into the following portfolio segments: Oil & Gas Proppants and Industrial & Specialty Products, which also aligns with our reporting segments. We estimate the allowance for credit losses based on historical collection trends, the age of outstanding receivables, risks attributable to specific customers, such as credit history, bankruptcy or other going concern issues, and current economic and industry conditions. If events or circumstances indicate that specific receivable balances may be impaired, further consideration is given to the collectability of those balances and the allowance is adjusted accordingly. Past due balances are written off when we have exhausted our internal and external collection efforts and have been unsuccessful in collecting the amount due. The following table reflects the change of the allowance for credit losses (in thousands) during the year ended December 31, 2020, disaggregated by portfolio segments: Oil & Gas Proppants Industrial & Specialty Products Total Beginning balance, December 31, 2019 $ 7,640 $ 1,344 $ 8,984 Provision for credit losses 1,340 170 1,510 Write-offs (3,296) (594) (3,890) Ending balance, December 31, 2020 $ 5,684 $ 920 $ 6,604

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2020
Inventory Disclosure [Abstract]
Schedule of Inventories	At December 31, 2020 and December 31, 2019, inventories (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Supplies $ 42,329 $ 47,277 Raw materials and work in process 33,723 41,167 Finished goods 28,632 35,988 Total inventories $ 104,684 $ 124,432

Property, Plant and Mine Deve_2

Property, Plant and Mine Development (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Mine Development	At December 31, 2020 and December 31, 2019, property, plant and mine development (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Mining property and mine development $ 788,287 $ 794,899 Asset retirement cost 15,985 18,260 Land 54,710 57,082 Land improvements 76,002 73,203 Buildings 69,841 69,112 Machinery and equipment 1,171,382 1,152,898 Furniture and fixtures 4,071 4,068 Construction-in-progress 27,216 54,675 2,207,494 2,224,197 Accumulated depletion, depreciation, amortization and impairment charges (839,402) (706,610) Total property, plant and mine development, net $ 1,368,092 $ 1,517,587

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes in the Carrying Amount of Goodwill	The changes in the carrying amount of goodwill (in thousands) by business segment consisted of the following: Oil & Gas Proppants Segment Industrial & Specialty Products Segment Total Balance at December 31, 2018 86,100 175,240 261,340 EPMH acquisition and measurement period adjustment — 12,184 12,184 Balance at December 31, 2019 86,100 187,424 273,524 Impairment losses (86,100) — (86,100) EPMH acquisition adjustment (1) — (1,775) (1,775) Balance at December 31, 2020 $ — $ 185,649 $ 185,649 (1) During the first quarter of 2020, an adjustment was made in accordance with ASC 250 to correct an immaterial error to acquisition accounting. We reclassified $1.8 million between goodwill and deferred tax liabilities. There was no impact to the Consolidated Statements of Operations.
Schedule of Changes in the Carrying Amount of Definite-Lived Intangible Assets	The changes in the carrying amount of intangible assets (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Gross Carrying Amount Accumulated Amortization Impairments Net Gross Carrying Amount Accumulated Amortization Impairments Net Technology and intellectual property $ 71,052 $ (18,854) (1,373) $ 50,825 $ 86,183 $ (17,080) — $ 69,103 Customer relationships 66,999 (23,182) $ — 43,817 68,599 (18,737) (1,240) 48,622 Total definite-lived intangible assets: $ 138,051 $ (42,036) $ (1,373) $ 94,642 $ 154,782 $ (35,817) $ (1,240) $ 117,725 Trade names 65,390 — (1,150) 64,240 65,390 — — 65,390 Other 700 — — 700 700 — — 700 Total intangible assets: $ 204,141 $ (42,036) $ (2,523) $ 159,582 $ 220,872 $ (35,817) $ (1,240) $ 183,815
Schedule of Changes in the Carrying Amount of Indefinite-Lived Intangible Assets	The changes in the carrying amount of intangible assets (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Gross Carrying Amount Accumulated Amortization Impairments Net Gross Carrying Amount Accumulated Amortization Impairments Net Technology and intellectual property $ 71,052 $ (18,854) (1,373) $ 50,825 $ 86,183 $ (17,080) — $ 69,103 Customer relationships 66,999 (23,182) $ — 43,817 68,599 (18,737) (1,240) 48,622 Total definite-lived intangible assets: $ 138,051 $ (42,036) $ (1,373) $ 94,642 $ 154,782 $ (35,817) $ (1,240) $ 117,725 Trade names 65,390 — (1,150) 64,240 65,390 — — 65,390 Other 700 — — 700 700 — — 700 Total intangible assets: $ 204,141 $ (42,036) $ (2,523) $ 159,582 $ 220,872 $ (35,817) $ (1,240) $ 183,815
Schedule of Estimated Amortization Expense Related to Definite-Lived Intangible Assets	The estimated amortization expense related to definite-lived intangible assets (in thousands) for the five succeeding years is as follows: 2021 $ 9,623 2022 $ 9,608 2023 $ 9,603 2024 $ 9,605 2025 $ 9,603

Accounts Payable and Accrued _2

Accounts Payable and Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Payables and Accruals [Abstract]
Schedule of Accounts Payables and Accrued Liabilities	At December 31, 2020 and 2019, accounts payable and accrued liabilities (in thousands) consisted of the following: December 31, 2020 2019 Trade payables $ 90,564 $ 181,029 Accrued salaries and wages 7,432 12,385 Accrued vacation liability 2,499 3,053 Current portion of liability for pension and post-retirement benefits 1,338 2,993 Accrued healthcare liability 1,886 4,078 Accrued property taxes and sales taxes 5,136 4,070 Vendor incentives 4,782 26,617 Other accrued liabilities 8,283 14,012 Accounts payable and accrued liabilities $ 121,920 $ 248,237

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Debt	At December 31, 2020 and 2019, debt (in thousands) consisted of the following: December 31, 2020 December 31, 2019 Senior secured credit facility: Revolver expiring May 1, 2023 (4.19% at December 31, 2020 and 7.75% at December 31, 2019) $ 25,000 $ — Term Loan facility—final maturity May 1, 2025 (5.00% at December 31, 2020 and 5.81% December 31, 2019) 1,234,800 1,247,600 Less: Unamortized original issue discount (4,376) (5,412) Less: Unamortized debt issuance cost (20,259) (25,390) Note payable secured by royalty interest — 10,438 Insurance financing notes payable 4,187 5,055 Equipment notes payable — 87 Finance leases 350 70 Total debt 1,239,702 1,232,448 Less: current portion (42,042) (18,463) Total long-term portion of debt $ 1,197,660 $ 1,213,985
Schedule of Contractual Maturities of Debt	At December 31, 2020, contractual maturities of our senior secured Credit Facility (in thousands) are as follows: 2021 $ 12,800 2022 12,800 2023 12,800 2024 12,800 2025 1,183,600 Thereafter — Total $ 1,234,800

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Changes in Asset Retirement Obligations	Changes in the asset retirement obligations (in thousands) during the years ended December 31, 2020 and 2019 are as follows: December 31, 2020 December 31, 2019 Beginning balance $ 25,825 $ 18,413 Accretion 1,434 1,531 Additions and revisions of estimates (2,542) 5,881 Ending balance $ 24,717 $ 25,825

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Estimated Fair Values of Derivative Instruments	The following table summarizes the fair value of our derivative instruments (in thousands, except contract/notional amount). See Note M - Fair Value Accounting for more information regarding the estimated fair values of our derivative instruments at December 31, 2020 and 2019. December 31, 2020 December 31, 2019 Maturity Contract/Notional Carrying Fair Maturity Date Contract/Notional Carrying Fair LIBOR (1) interest rate swap agreement 2020 $440 million $ — $ — 2020 $440 million $ (2,768) $ (2,768) LIBOR (1) interest rate swap agreement 2020 $200 million $ — $ — 2020 $200 million $ (1,259) $ (1,259)
Schedule of Effect of Derivatives Instruments on Combined Statements of Operations and Comprehensive Income	The following table summarizes the effect of derivative instruments (in thousands) on our income statements and our consolidated statements of comprehensive income for the years ended December 31, 2020, 2019 and 2018: 2020 2019 2018 Deferred losses from derivatives in OCI, beginning of period $ (3,053) $ (1,621) $ (76) Gain (loss) recognized in OCI from derivative instruments 3,053 (1,432) (1,622) Loss reclassified from Accumulated OCI — — 77 Deferred losses from derivatives in OCI, end of period $ — $ (3,053) $ (1,621)

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Schedule of Stock Options Activity	The following table summarizes the status of, and changes in, our stock option awards during the year ended December 31, 2020: Number of Weighted Aggregate Intrinsic Value Weighted Outstanding at December 31, 2019 826,658 $ 28.97 $ 11,557 4.1 years Granted — — — Exercised — — — Forfeited (443) 32.41 — Expired — $ — $ — Outstanding at December 31, 2020 826,215 $ 29.05 $ — 3.1 years Exercisable at December 31, 2020 826,215 $ 29.05 $ — 3.1 years
Schedule of Restricted Stock, Restricted Stock Unit and Performance Share Unit Awards Activity	The following table summarizes the status of, and changes in, our unvested restricted stock awards during the year ended December 31, 2020: Number of Shares Grant Date Weighted Unvested, December 31, 2019 1,020,248 $ 15.86 Granted 1,590,170 4.09 Vested (539,614) 15.98 Forfeited (290,978) 10.66 Unvested, December 31, 2020 1,779,826 $ 6.22 The following table summarizes the status of, and changes in, our performance share unit awards during the year ended December 31, 2020: Number of Shares Grant Date Weighted Unvested, December 31, 2019 838,722 $ 18.00 Granted 1,020,161 6.57 Vested — — Forfeited/Cancelled (345,235) 24.23 Unvested, December 31, 2020 1,513,648 $ 12.36

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Annual Commitments	Future Minimum Annual Commitments at December 31, 2020 (in thousands): Year ending December 31, Minimum Purchase Commitments 2021 $ 14,812 2022 10,328 2023 10,328 2024 7,020 2025 2,654 Thereafter 6,604 Total future purchase commitments $ 51,746

Pension and Post-Retirement B_2

Pension and Post-Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Schedule of Net Pension Benefit Cost	Net pension benefit cost (in thousands) consisted of the following for the years ended December 31, 2020, 2019 and 2018: Year Ended 2020 2019 2018 Service cost $ 2,253 $ 1,304 $ 1,307 Interest cost 4,037 5,375 4,632 Expected return on plan assets (6,019) (6,171) (5,969) Net amortization and deferral 3,127 1,648 2,526 Net pension benefit costs $ 3,398 $ 2,156 $ 2,496 Net post-retirement benefit cost (in thousands) consisted of the following for the years ended December 31, 2020, 2019 and 2018: Year Ended December 31, 2020 2019 2018 Service cost $ 70 $ 88 $ 102 Interest cost 584 789 740 Unrecognized net (gain)/loss — (29) — Net post-retirement benefit costs $ 654 $ 848 $ 842
Schedule of Changes in Benefit Obligations and Plan Assets	The changes in benefit obligations and plan assets (in thousands), as well as the funded status (in thousands) of our pension and post-retirement plans at December 31, 2020 and 2019 are as follows: Pension Benefits Post-retirement Benefits 2020 2019 2020 2019 Benefit obligation at January 1, $ 148,491 $ 138,900 $ 22,054 $ 21,570 Service cost 2,253 1,304 70 88 Interest cost 4,037 5,375 584 789 Actuarial (gain) loss 11,119 17,225 1,329 206 Benefits paid (8,649) (14,922) (1,751) (815) Other (1) (53) 609 (10,968) 216 Benefit obligation at December 31, $ 157,198 $ 148,491 $ 11,318 $ 22,054 Fair value of plan assets at January 1, $ 110,431 $ 102,396 $ — $ — Actual return on plan assets 13,306 17,919 — — Employer contributions 5,475 4,755 1,335 599 Benefits paid (8,649) (14,922) (1,751) (815) Other (1) — 283 416 216 Fair value of plan assets at December 31, $ 120,563 $ 110,431 $ — $ — Plan assets less than benefit obligations at December 31 recognized as liability for pension and other post-retirement benefits $ (36,635) $ (38,060) $ (11,318) $ (22,054) (1) Includes opening pension benefit obligation and plan assets balances related to the May 1, 2018, EPMH acquisition
Schedule of Estimated Future Pension and Post-Retirement Benefit Payments	Future estimated annual benefit payments (in thousands) for pension and post-retirement benefit obligations at December 31, 2020 are as follows: Benefits Post-retirement Pension Before After 2021 $ 9,329 $ 1,217 $ 1,217 2022 9,346 1,095 1,095 2023 9,326 1,002 1,002 2024 9,678 959 959 2025 9,224 883 883 2026-2030 44,832 3,393 3,393
Schedule of Weighted-Average Assumptions Used to Determine Benefit Obligations	The following weighted-average assumptions were used to determine our obligations under the plans: Pension Benefits Post-retirement Benefits 2020 2019 2020 2019 Discount rate 2.5 % 3.2 % 2.1 % 3.2 % Long-term rate of compensation increase 3.0% 3.0%-3.5% N/A N/A Long-term rate of return on plan assets 6.3 % 6.3% N/A N/A Health care cost trend rate: Pre-65 initial rate/ultimate rate N/A N/A 6.5%/4.5% 7.0%/4.5% Pre-65 ultimate year N/A N/A 2028 2026 Post-65 initial rate/ultimate rate N/A N/A 7.0%/4.5% 7.5%/4.5% Post-65 ultimate year N/A N/A 2028 2027
Schedule of Mortality Tables Used	Mortality tables used for pension benefits and post-retirement benefits plans are the following: Pension and Post-retirement Benefits 2020 2019 Healthy Lives Pri-2012 base mortality tables with generational mortality improvements using Scale MP-2020 Pri-2012 base mortality tables with generational mortality improvements using Scale MP-2019 Disabled Lives Pri-2012 base mortality tables with generational mortality improvements using Scale MP-2020 Pri-2012 base mortality tables with generational mortality improvements using Scale MP-2019
Schedule of Major Investments Categories and Their Relative Percentage of the Fair Value to Total Plan Assets	The major investment categories and their relative percentage of the fair value of total plan assets as invested at December 31, 2020, and 2019 were as follows: Pension Benefits Post-retirement Benefits (1) 2020 2019 2020 2019 Equity securities 57.9 % 52.1 % — % — % Debt securities 41.3 % 46.6 % — % — % Cash 0.8 % 1.3 % — % — % (1) Retiree health benefits are paid by the Company as covered expenses are incurred.
Schedule of Fair Value of Pension Plan Assets by Asset Category	The fair values of the pension plan assets (in thousands) at December 31, 2020, by asset category, were as follows: Level 1 Level 2 Level 3 Total Cash and cash equivalents $ — $ 1,020 $ — $ 1,020 Mutual funds: Diversified emerging markets 7,064 — — 7,064 Foreign large blend 22,638 — — 22,638 Large-cap blend 22,272 — — 22,272 Mid-cap blend 12,972 — — 12,972 Real estate 4,822 — — 4,822 Fixed income securities: Corporate notes and bonds 38,983 — — 38,983 U.S. Treasuries 8,582 — — 8,582 Mortgage-backed securities — 1,780 — 1,780 Asset-backed securities — 430 — 430 Net asset $ 117,333 $ 3,230 $ — $ 120,563 The fair values of the pension plan assets (in thousands) at December 31, 2019, by asset category, were as follows: Level 1 Level 2 Level 3 Total Cash and cash equivalents $ — $ 1,385 $ — $ 1,385 Mutual funds: Diversified emerging markets 4,942 — — 4,942 Foreign large blend 19,183 — — 19,183 Large-cap blend 20,738 — — 20,738 Mid-cap blend 8,416 — — 8,416 Real estate 4,309 — — 4,309 Fixed income securities: Corporate notes and bonds 37,664 — — 37,664 U.S. Treasuries 10,894 — — 10,894 Mortgage-backed securities — 2,496 — 2,496 Asset-backed securities — 404 — 404 Net asset $ 106,146 $ 4,285 $ — $ 110,431
Schedule of Summary of Multiemployer Pension Plan	A summary of each multiemployer pension plan for which we participate is presented below: Pension EIN/ Pension Pension Protection Act Zone Status (1) FIP/RP Status Company Surcharge Expiration 2020 2019 2020 2019 2018 LIUNA 52-6074345/001 Green Red No $ 361 $ 385 $ 573 No 6/4/2022 IUOE 36-6052390/001 Green Green No 256 310 1,385 No 7/31/2022 CSSS (2) 36-6044243/001 Red Red Yes 51 51 51 NA NA (1) The Pension Protection Act of 2006 defines the zone status as follows: green—healthy, yellow—endangered, orange—seriously endangered and red—critical. (2) In 2011, we withdrew from the Central States, Southeast and Southwest Areas Pension Plan. The withdrawal liability of $1.0 million will be paid in monthly installments of $4,000 until 2031.

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of Supplemental Balance Sheet Information	Supplemental balance sheet information related to leases (in thousands except for term and rate information) was as follows: Leases Classification December 31, 2020 December 31, 2019 Assets Operating Operating lease right-of-use assets $ 37,469 $ 53,098 Finance Property, plant and mine development, net 339 — Total leased assets $ 37,808 $ 53,098 Liabilities Current Operating Current portion of operating lease liabilities $ 17,388 $ 53,587 Finance Current portion of long-term debt 55 — Non-Current Operating Operating lease liabilities 76,361 117,964 Finance Long-term debt, net 295 — Total lease liabilities $ 94,099 $ 171,551 We recorded impairment charges related to railcar leases, various equipment leases and an office building lease. These charges relate to the Oil & Gas Proppants segment and are recorded in "Goodwill and other asset impairments" in the Consolidated Statements of Operations. See Note Y - Impairments for additional information. During the year ended 2020, we received lease concessions from certain lessors. Based on accounting elections provided by the FASB and in accordance with ASC 842-10, we have not accounted for these concessions as lease modifications. Based on remeasurement of the amended leases, for the year ended December 31, 2020, we recorded a decrease to the ROU assets of $1.0 million and a decrease to the liability of $25.0 million. A gain of $24.0 million was recognized as operating income through cost of goods sold in our consolidated income statement for the year ended December 31, 2020. Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. As most of our leases do not provide an implicit rate, in determining the lease liability and the present value of lease payments, we used our incremental borrowing rate based on the information available at the lease commencement date. The weighted average remaining lease term and discount rate as of December 31, 2020 and 2019 related to leases are as follows: Lease Term and Discount Rate December 31, 2020 December 31, 2019 Weighted average remaining lease term: Operating leases 6.9 years 4.5 years Finance leases 2.9 years N/A Weighted average discount rate: Operating leases 5.8 % 5.7 % Finance leases 5.0 % — %
Schedule of Components of Lease Expense and Supplemental Cash Flow Information	The components of lease expense included in our Consolidated Statements of Operations were as follows: Lease Costs Classification Year Ended Year Ended Operating lease costs (1) Cost of Sales $ 26,548 88,966 Operating lease costs (2) Selling, general, and administrative 1,808 3,993 Right-of-use asset impairment Goodwill and other asset impairments 3,406 115,443 Total (3) $ 31,762 208,402 (1) Includes short-term operating lease costs of $9.6 million and $18.2 million for the years ended December 31, 2020 and 2019, respectively. (2) Includes short-term operating lease costs of $0.4 million and $0.7 million for the years ended December 31, 2020 and 2019, respectively. (3) Does not include expense for the year ended December 31, 2020 of $12 thousand for finance leases. Supplemental cash flow information related to leases was as follows: Year Ended December 31, 2020 Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 62,140 $ 74,740 Operating cash flows for finance leases $ 12 $ — Right-of-use assets obtained in exchange for new lease liabilities: Operating leases $ 10,747 $ 232,123 Finance leases $ 359 $ —
Schedule of Maturity of Operating Lease Liabilities	Maturities of lease liabilities as of December 31, 2020: Maturities of lease liabilities Operating leases Finance leases 2021 $ 23,217 $ 71 2022 16,447 71 2023 16,019 244 2024 14,181 — 2025 11,617 — Thereafter 38,205 — Total lease payments $ 119,686 386 Less: Interest 20,984 36 Less: Other operating expenses 4,953 — Total $ 93,749 350
Schedule of Maturities of Finance Lease Liabilities	Maturities of lease liabilities as of December 31, 2020: Maturities of lease liabilities Operating leases Finance leases 2021 $ 23,217 $ 71 2022 16,447 71 2023 16,019 244 2024 14,181 — 2025 11,617 — Thereafter 38,205 — Total lease payments $ 119,686 386 Less: Interest 20,984 36 Less: Other operating expenses 4,953 — Total $ 93,749 350

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Income Tax Benefit (Expense)	Income tax benefit (in thousands) consisted of the following for the years ended December 31, 2020, 2019 and 2018: Year ended December 31, 2020 2019 2018 Current: Federal $ — $ — $ 1,076 State (307) (1,188) (2,496) Foreign (1,473) (1,343) (518) (1,780) (2,531) (1,938) Deferred: Federal 57,214 90,457 25,578 State 4,591 11,225 5,492 Foreign — — — 61,805 101,682 31,070 Income tax benefit $ 60,025 $ 99,151 $ 29,132
Schedule of Effective Income Tax Rate on Pretax Earnings	Income tax benefit (in thousands) differed from the amount that would be provided by applying the U.S. federal statutory rate for the years ended December 31, 2020, 2019 and 2018 due to the following: Year ended December 31, 2020 2019 2018 Income tax (expense) benefit computed at U.S. federal statutory rate $ 36,781 $ 90,070 $ 48,290 Decrease (increase) resulting from: Statutory depletion 1,230 4,679 12,090 Goodwill impairment — — (29,157) Prior year tax return reconciliation (2,084) 3,121 530 State income taxes, net of federal benefit 5,013 9,486 2,592 Adjustment to deferred taxes from the CARES Act 22,318 — — Equity compensation (1,477) (6,440) (653) Other, net (1,756) (1,765) (4,560) Income tax benefit $ 60,025 $ 99,151 $ 29,132
Schedule of Tax Effects on Deferred Tax Assets and Liabilities	The tax effects of the types of temporary differences and carry forwards that gave rise to deferred tax assets and liabilities (in thousands) at December 31, 2020 and 2019 consisted of the following: December 31, 2020 2019 Gross deferred tax assets: Net operating loss carry forward and state tax credits $ 90,087 $ 32,173 Pension and post-retirement benefit costs 11,146 13,976 Alternative minimum tax credit carry forward — 7,895 Property, plant and equipment 6,866 7,179 Accrued expenses 12,397 15,336 Inventories 121 6,507 Federal tax credits 4,188 — Stock-based compensation expense 4,307 2,390 Interest expense limitation 14,127 22,324 Intangibles 11,304 — Lease obligation liability 14,154 29,604 Other 5,286 5,536 Total deferred tax assets 173,983 142,920 Gross deferred tax liabilities: Land and mineral property basis difference (122,265) (124,182) Fixed assets and depreciation (100,640) (44,314) Intangibles — (12,541) Other (464) (468) Total deferred tax liabilities (223,369) (181,505) Net deferred tax liabilities $ (49,386) $ (38,585)

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Schedule of Sales by Major Source	The following table reflects our sales disaggregated by major source for the years ended December 31, 2020 and 2019 (in thousands): Year Ended December 31, 2020 Year Ended December 31, 2019 Category Oil & Gas Proppants Industrial & Specialty Products Total Sales Oil & Gas Proppants Industrial & Specialty Products Total Sales Product $ 301,199 $ 430,988 $ 732,187 $ 704,516 $ 463,956 $ 1,168,472 Service 113,698 — 113,698 306,005 — 306,005 Total Sales $ 414,897 $ 430,988 $ 845,885 $ 1,010,521 $ 463,956 $ 1,474,477
Schedule of Changes in Contract Assets and Liabilities	The following tables reflect the changes in our contract assets, which we classify as unbilled receivables and our contract liabilities, which we classify as deferred revenues, for the years ended December 31, 2020 and 2019 (in thousands): Unbilled Receivables December 31, 2020 December 31, 2019 Beginning Balance $ 20,144 $ 90 Reclassifications to billed receivables (10,330) (3,983) Revenues recognized in excess of period billings 38,168 24,037 Ending Balance $ 47,982 $ 20,144 We enter into certain customer supply agreements which give the customers the right to purchase certain products for a discounted price at certain volumes over an average initial contract term of one Deferred Revenue December 31, 2020 December 31, 2019 Beginning Balance $ 50,634 $ 113,319 Revenues recognized from balances held at the beginning of the period (19,704) (65,225) Revenues deferred from period collections on unfulfilled performance obligations 6,627 12,225 Revenues recognized from period collections (3,865) (9,685) Ending Balance $ 33,692 $ 50,634
Schedule of Information Related to Foreign Operations	The following table includes information related to our foreign operations for the years ended December 31, 2020, 2019, and 2018 (in thousands): December 31, 2020 December 31, 2019 December 31, 2018 Total Sales $ 86,179 $ 92,788 $ 66,917 Pre-tax income $ 8,509 $ 7,010 $ 5,901 Net income $ 6,722 $ 5,538 $ 4,662

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Schedule of Sales and Segment Contribution Margin for Reporting Segments and Operating Results	The following table presents sales and segment contribution margin (in thousands) for the reportable segments and other operating results not allocated to the reported segments for the years ended December 31, 2020, 2019 and 2018: Year Ended 2020 2019 2018 Sales: Oil & Gas Proppants $ 414,897 $ 1,010,521 $ 1,182,991 Industrial & Specialty Products 430,988 463,956 394,307 Total sales 845,885 1,474,477 1,577,298 Segment contribution margin: Oil & Gas Proppants 142,041 248,594 357,846 Industrial & Specialty Products 159,176 178,215 155,084 Total segment contribution margin 301,217 426,809 512,930 Operating activities excluded from segment cost of sales (1) (30,402) (85,625) (98,761) Selling, general and administrative (124,171) (150,848) (146,971) Depreciation, depletion and amortization (155,568) (179,444) (148,832) Goodwill and other asset impairments (110,688) (363,847) (281,899) Interest expense (79,885) (95,472) (70,564) Other income (expense), net, including interest income 24,350 19,519 4,144 Income tax benefit 60,025 99,151 29,132 Net loss $ (115,122) $ (329,757) $ (200,821) Less: Net loss attributable to non-controlling interest (1,028) (675) (13) Net loss attributable to U.S. Silica Holdings, Inc. $ (114,094) $ (329,082) $ (200,808) (1) 2019 and 2018 mainly driven by plant capacity expansion expenses, amortization of purchase accounting inventory fair value step-up, and facility closure costs.

Unaudited Supplementary Data (T

Unaudited Supplementary Data (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Schedule of Unaudited Quarterly Information	The following table sets forth our unaudited quarterly consolidated statements of operations (in thousands, except per share data) for each of the four quarters in the years ended December 31, 2020 and 2019. This unaudited quarterly information has been prepared on the same basis as our annual audited financial statements and includes all adjustments, consisting only of normal recurring adjustments that are necessary to present fairly the financial information for the fiscal quarters presented. First Second Third Fourth 2020 (Unaudited) Sales: Product $ 222,161 $ 160,200 $ 159,637 $ 190,189 Service 47,438 12,337 16,835 37,088 Cost of sales (excluding depreciation, depletion and amortization): Product 165,496 114,130 93,747 113,609 Service 35,821 10,613 13,845 27,809 Operating expenses: Selling, general and administrative 30,052 39,126 27,216 27,777 Depreciation, depletion and amortization 38,449 37,086 40,069 39,964 Goodwill and other asset impairments 103,866 3,956 222 2,644 Total operating expenses 172,367 80,168 67,507 70,385 Operating (loss) income (104,085) (32,374) 1,373 15,474 Other (expense) income: Interest expense (22,277) (22,179) (19,274) (16,155) Other income (expense), net, including interest income 17,671 (1,670) (409) 8,758 Total other expense (4,606) (23,849) (19,683) (7,397) (Loss) income before income taxes (108,691) (56,223) (18,310) 8,077 Income tax benefit (expense) 36,086 23,605 4,094 (3,760) Net (loss) income (72,605) (32,618) (14,216) 4,317 Less: Net loss attributable to non-controlling interest (260) (264) (254) (250) Net (loss) income attributable to U.S. Silica Holdings, Inc. $ (72,345) $ (32,354) $ (13,962) $ 4,567 (Loss) earnings per share, basic $ (0.98) $ (0.44) $ (0.19) $ 0.06 (Loss) earnings per share, diluted $ (0.98) $ (0.44) $ (0.19) $ 0.06 Weighted average shares outstanding, basic 73,467 73,620 73,688 73,728 Weighted average shares outstanding, diluted 73,467 73,620 73,688 74,328 Dividends declared per share $ 0.02 $ — $ — $ — First Second Third Fourth 2019 (Unaudited) Sales: Product $ 296,860 $ 303,041 $ 287,977 $ 280,594 Service 81,890 91,813 73,837 58,465 Cost of sales (excluding depreciation, depletion and amortization): Product 234,916 225,473 226,797 212,905 Service 62,622 68,687 56,836 45,057 Operating expenses: Selling, general and administrative 34,656 38,659 40,208 37,325 Depreciation, depletion and amortization 44,600 44,899 47,126 42,819 Goodwill and other asset impairments — — 130 363,717 Total operating expenses 79,256 83,558 87,464 443,861 Operating income (loss) 1,956 17,136 (9,283) (362,764) Other (expense) income: Interest expense (23,978) (23,765) (24,733) (22,996) Other income, net, including interest income 722 15,074 3,280 443 Total other expense (23,256) (8,691) (21,453) (22,553) (Loss) income before income taxes (21,300) 8,445 (30,736) (385,317) Income tax benefit (expense) 1,972 (2,384) 7,671 91,892 Net (loss) income (19,328) 6,061 (23,065) (293,425) Less: Net loss attributable to non-controlling interest (4) (89) (28) (554) Net (loss) income attributable to U.S. Silica Holdings, Inc. $ (19,324) $ 6,150 $ (23,037) $ (292,871) (Loss) earnings per share, basic $ (0.26) $ 0.08 $ (0.31) $ (4.00) (Loss) earnings per share, diluted $ (0.26) $ 0.08 $ (0.31) $ (4.00) Weighted average shares, basic 73,040 73,301 73,328 73,343 Weighted average shares, diluted 73,040 73,505 73,328 73,343 Dividends declared per share $ 0.06 $ 0.06 $ 0.06 $ 0.06

Parent Company Financials (Tabl

Parent Company Financials (Tables)	12 Months Ended
	Dec. 31, 2020
Condensed Financial Information Disclosure [Abstract]
Condensed Balance Sheets	U.S. SILICA HOLDINGS, INC. (PARENT COMPANY ONLY) CONDENSED BALANCE SHEETS December 31, 2020 2019 (in thousands) ASSETS Current Assets: Cash and cash equivalents $ 46,851 $ 51,849 Due from affiliates 168,276 138,988 Total current assets 215,127 190,837 Investment in subsidiaries 412,169 530,830 Total assets $ 627,296 $ 721,667 LIABILITIES AND STOCKHOLDERS’ EQUITY Current Liabilities: Accrued expenses and other current liabilities $ 286 $ 129 Dividends payable 219 4,958 Total current liabilities 505 5,087 Total liabilities 505 5,087 Stockholders’ Equity: Preferred stock — — Common stock 827 823 Additional paid-in capital 1,200,023 1,185,116 Retained deficit (395,496) (279,956) Treasury stock, at cost (181,615) (180,912) Accumulated other comprehensive loss (8,479) (19,854) Total U.S. Silica Holdings, Inc. stockholders’ equity 615,260 705,217 Non-controlling interest 11,531 11,363 Total stockholders' equity 626,791 716,580 Total liabilities and stockholders’ equity $ 627,296 $ 721,667
Condensed Statements of Operations and Comprehensive Income (Loss)	U.S. SILICA HOLDINGS, INC. (PARENT COMPANY ONLY) CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) Year ended December 31, 2020 2019 2018 (in thousands) Sales $ — $ — $ — Cost of sales — — — Operating expenses Selling, general and administrative 253 253 254 Total operating expenses 253 253 254 Operating loss (253) (253) (254) Other income (expense) Interest income 210 1,440 2,784 Total other income 210 1,440 2,784 (Loss) income before income taxes and equity in net earnings of subsidiaries (43) 1,187 2,530 Income tax expense — (327) (696) (Loss) income before equity in net earnings of subsidiaries (43) 860 1,834 Equity in earnings of subsidiaries, net of tax (115,079) (330,617) (202,655) Net loss (115,122) (329,757) (200,821) Less: Net loss attributable to non-controlling interest (1,028) (675) (13) Net loss attributable to U.S. Silica Holdings, Inc. (114,094) (329,082) (200,808) Net loss (115,122) (329,757) (200,821) Other comprehensive (loss) income Unrealized loss on derivatives (net of tax of $973, $(456), and $(470) for 2020, 2019, and 2018, respectively) 3,053 (1,432) (1,545) Foreign currency translation adjustment (net of tax of $444, $(60), and $(196) for 2020, 2019 and 2018, respectively) 1,391 (188) (614) Pension and other post-retirement benefits liability adjustment (net of tax of $2,207, $(1,024), and $339 for 2020, 2019 and 2018, respectively) 6,931 (3,214) 1,065 Comprehensive loss (103,747) (334,591) (201,915) Less: Comprehensive loss attributable to non-controlling interest (1,028) (675) (13) Comprehensive loss attributable to U.S. Silica Holdings, Inc. (102,719) (333,916) (201,902)
Condensed Statements of Stockholders' Equity	U.S. SILICA HOLDINGS, INC. (PARENT COMPANY ONLY) CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY (amounts in thousands) Par Value Treasury Stock Additional Paid-In Capital Retained Earnings - Present Accumulated Other Comprehensive Income (Loss) Total U.S. Silica, Inc. Stockholders' Equity Non-controlling Interest Total Balance at January 1, 2018 $ 812 $ (25,456) $ 1,147,084 $ 287,992 $ (13,926) $ 1,396,506 $ — $ 1,396,506 Net loss — — — (200,808) — (200,808) (13) (200,821) Unrealized loss on derivatives — — — — (1,545) (1,545) — (1,545) Foreign currency translation adjustment — — — — (614) (614) — (614) Pension and post-retirement liability — — — — 1,065 1,065 — 1,065 Cash dividend declared ($0.25 per share) — — — (19,330) — (19,330) — (19,330) Common stock-based compensation plans activity: Equity-based compensation — — 22,337 — — 22,337 — 22,337 Proceeds from options exercised — 93 (32) — — 61 — 61 Shares withheld for employee taxes related to vested restricted stock and stock units 6 (4,383) (6) — — (4,383) — (4,383) Repurchase of common stock (148,469) (148,469) — (148,469) Balance at December 31, 2018 $ 818 $ (178,215) $ 1,169,383 $ 67,854 $ (15,020) $ 1,044,820 $ 7,484 $ 1,052,304 Net loss — — — (329,082) — (329,082) (675) (329,757) Unrealized loss on derivatives — — — — (1,432) (1,432) — (1,432) Foreign currency translation adjustment — — — — (188) (188) — (188) Pension and post-retirement liability — — — — (3,214) (3,214) — (3,214) Cash dividend declared ($0.25 per share) — — — (18,728) — (18,728) — (18,728) Contributions from non-controlling interest — — — — — — 4,554 4,554 Common stock-based compensation plans activity: Equity-based compensation — — 15,906 — — 15,906 — 15,906 Proceeds from options exercised — 296 (168) — — 128 — 128 Shares withheld for employee taxes related to vested restricted stock and stock units 5 (2,993) (5) — — (2,993) — (2,993) Balance at December 31, 2019 $ 823 $ (180,912) $ 1,185,116 $ (279,956) $ (19,854) $ 705,217 $ 11,363 $ 716,580 Net loss — — — (114,094) — (114,094) (1,028) (115,122) Unrealized gain on derivatives — — — — 3,053 3,053 — 3,053 Foreign currency translation adjustment — — — — 1,391 1,391 — 1,391 Pension and post-retirement liability — — — — 6,931 6,931 — 6,931 Cash dividend declared ($0.02 per share) — — — (1,446) — (1,446) — (1,446) Contributions from non-controlling interest — — — — — — 1,196 1,196 Common stock-based compensation plans activity: Equity-based compensation — — 14,911 — — 14,911 — 14,911 Shares withheld for employee taxes related to vested restricted stock and stock units 4 (703) (4) — — (703) — (703) Balance at December 31, 2020 $ 827 $ (181,615) $ 1,200,023 $ (395,496) $ (8,479) $ 615,260 $ 11,531 $ 626,791
Condensed Statements of Cash Flows	U.S. SILICA HOLDINGS, INC. (PARENT COMPANY ONLY) CONDENSED STATEMENTS OF CASH FLOWS Year ended December 31, 2020 2019 2018 (in thousands) Operating activities: Net loss $ (115,122) $ (329,757) $ (200,821) Adjustments to reconcile net (loss) income to net cash provided by operating activities: Undistributed loss (income) from equity method investment, net 115,079 330,617 202,655 Changes in assets and liabilities, net of effects of acquisitions: Accounts payable and accrued liabilities 155 (88) (295) Net cash provided by operating activities 112 772 1,539 Investing activities: Investment in subsidiary — — — Net cash used in investing activities — — — Financing activities: Dividends paid (6,185) (18,592) (19,912) Repurchase of common stock — — (148,469) Proceeds from options exercised — 128 61 Tax payments related to shares withheld for vested restricted stock and stock units (703) (2,993) (4,383) Contributions from non-controlling interest 1,196 4,554 7,497 Net financing activities with subsidiaries 582 (39,171) 40,171 Net cash used in financing activities (5,110) (56,074) (125,035) Net decrease in cash and cash equivalents (4,998) (55,302) (123,496) Cash and cash equivalents, beginning of period 51,849 107,151 230,647 Cash and cash equivalents, end of period $ 46,851 $ 51,849 $ 107,151 Supplemental cash flow information: Cash (received) paid during the period for: Interest $ (210) $ (1,440) $ (2,784)

Impairments (Tables)

Impairments (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Text Block Supplement [Abstract]
Schedule of Asset Impairment Charges	We recorded impairment charges (in thousands) for the years ended December 31, 2020, 2019 and 2018 for the following assets: Description December 31, 2020 December 31, 2019 December 31, 2018 Inventories, net $ 6,837 $ 4,100 $ 3,316 Property, plant and mine development, net 11,822 243,064 109,938 Operating lease right-of-use assets 3,406 115,443 — Goodwill 86,100 — 164,167 Intangible assets, net 2,523 1,240 4,478 Total $ 110,688 $ 363,847 $ 281,899

Organization (Details)

Organization (Details) $ in Thousands	May 01, 2018USD ($)	Dec. 31, 2020USD ($)Segment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Organization And Nature Of Business
Number of business segments | Segment		2
Consideration paid, net of cash acquired		$ 0	$ 0	$ 743,249
EPMH
Organization And Nature Of Business
Consideration paid, net of cash acquired	$ 743,200
Cash acquired	19,100
Net working capital post-closing adjustments	$ 500

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Water rights intangibles acquired in VIE		$ 456	$ 3,932	$ 10,046
Assets		2,246,947	2,553,234
Liabilities		$ 1,620,156	1,836,654
Percent or reporting unit fair value less than carrying value		50.00%
Amortization of debt issuance costs and discounts included in interest expense		$ 5,100	5,600	$ 4,000
Self-insurance reserves		4,800	6,600
Self-insurance reserves classified as current		$ 1,800	$ 4,100
Restricted Stock and Restricted Stock Units
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting period for awards of equity instruments		3 years
Performance Share Units
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting period for awards of equity instruments		3 years
Performance Share Units | Certain Employees
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting period for awards of equity instruments			3 years
Intellectual property
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful live of finite-lived intangible assets		15 years
Buildings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of property, plant and mine equipment		15 years
Land improvements
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of property, plant and mine equipment		10 years
Furniture and fixtures
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of property, plant and mine equipment		8 years
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Self-insurance retention amount		$ 100
Minimum | Supply Agreement
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, average initial contract term		1 year
Minimum | Stock options excluded
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting period for awards of equity instruments		3 years
Minimum | Customer relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful live of finite-lived intangible assets		13 years
Minimum | Machinery and equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of property, plant and mine equipment		3 years
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Self-insurance retention amount		$ 500
Maximum | Supply Agreement
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, average initial contract term		15 years
Maximum | Stock options excluded
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting period for awards of equity instruments		4 years
Maximum | Customer relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful live of finite-lived intangible assets		20 years
Maximum | Machinery and equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of property, plant and mine equipment		10 years
Variable Interest Entity, Primary Beneficiary
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity ownership percentage acquired in VIE	50.00%
Payments to acquire interest in VIE	$ 3,200
Maximum capital contribution to VIE	7,000
Assets		$ 17,300
Liabilities		100
Capital contributions paid to acquire interest in VIE		$ 200	$ 400
Variable Interest Entity, Primary Beneficiary | Water rights
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Water rights intangibles acquired in VIE	$ 700

Earnings Per Share - Computatio

Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss attributable to U.S. Silica Holdings, Inc.	$ 4,567	$ (13,962)	$ (32,354)	$ (72,345)	$ (292,871)	$ (23,037)	$ 6,150	$ (19,324)	$ (114,094)	$ (329,082)	$ (200,808)
Denominator:
Weighted average shares outstanding (shares)	73,728	73,688	73,620	73,467	73,343	73,328	73,301	73,040	73,634	73,253	76,453
Diluted effect of stock awards (shares)									0	0	0
Weighted average shares outstanding assuming dilution (shares)									73,634	73,253	76,453
Loss per share attributable to U.S. Silica Holdings, Inc.:
Basic loss per share (in dollars per share)	$ 0.06	$ (0.19)	$ (0.44)	$ (0.98)	$ (4)	$ (0.31)	$ 0.08	$ (0.26)	$ (1.55)	$ (4.49)	$ (2.63)
Diluted loss per share (in dollars per share)	$ 0.06	$ (0.19)	$ (0.44)	$ (0.98)	$ (4)	$ (0.31)	$ 0.08	$ (0.26)	$ (1.55)	$ (4.49)	$ (2.63)

Earnings Per Share - Antidiluti

Earnings Per Share - Antidilutive Securities Excluded From Calculation of Diluted Earnings (Loss) Per Common Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Potentially dilutive shares excluded
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from the calculation of diluted earnings (loss) per common share (shares)	238	68	443
Stock options excluded
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from the calculation of diluted earnings (loss) per common share (shares)	826	711	574
Restricted stock and performance share units awards excluded
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from the calculation of diluted earnings (loss) per common share (shares)	3,435	1,298	155

Capital Structure and Accumul_3

Capital Structure and Accumulated Other Comprehensive Income (Loss) - Narrative (Details) - USD ($)	3 Months Ended								12 Months Ended			31 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	May 31, 2018
Capital Structure And Accumulated Comprehensive Income (Loss)
Common stock authorized (shares)	500,000,000				500,000,000				500,000,000	500,000,000		500,000,000
Common stock, par value (in dollars per share)	$ 0.01				$ 0.01				$ 0.01	$ 0.01		$ 0.01
Common stock issued (shares)	83,143,176				82,601,926				83,143,176	82,601,926		83,143,176
Common stock outstanding (shares)	73,986,566				73,601,950				73,986,566	73,601,950		73,986,566
Preferred stock authorized (shares)	10,000,000				10,000,000				10,000,000	10,000,000		10,000,000
Preferred stock, par value (in dollars per share)	$ 0.01				$ 0.01				$ 0.01	$ 0.01		$ 0.01
Preferred stock issued (shares)	0				0				0	0		0
Preferred stock outstanding (shares)	0				0				0	0		0
Dividends declared per share (in dollars per share)	$ 0	$ 0	$ 0	$ 0.02	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.02	$ 0.25	$ 0.25
May 2018 Share Repurchase Program
Capital Structure And Accumulated Comprehensive Income (Loss)
Share repurchase program authorized amount													$ 200,000,000
Repurchase of common stock (shares)									0			5,036,139
Average price per common share of repurchase common stock (in dollars per share)												$ 14.59
Remaining authorized repurchase amount	$ 126,500,000								$ 126,500,000			$ 126,500,000

Capital Structure and Accumul_4

Capital Structure and Accumulated Other Comprehensive Income (Loss) - Declared Quarterly Cash Dividends (Details)	Feb. 10, 2020$ / shares
Equity [Abstract]
Dividends per Common Share (in dollars per share)	$ 0.02

Capital Structure and Accumul_5

Capital Structure and Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 716,580	$ 1,052,304	$ 1,396,506
Other comprehensive income before reclassifications	8,981
Amounts reclassed from accumulated other comprehensive loss	2,394
Ending Balance	626,791	716,580	1,052,304
Unrealized income (loss) on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(3,053)	(1,621)	(76)
Other comprehensive income before reclassifications	3,053	(1,432)	(1,622)
Amounts reclassed from accumulated other comprehensive loss	0
Ending Balance	0	(3,053)	(1,621)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(808)
Other comprehensive income before reclassifications	1,391
Amounts reclassed from accumulated other comprehensive loss	0
Ending Balance	583	(808)
Pension and other post-retirement benefits liability
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(15,993)
Other comprehensive income before reclassifications	4,537
Amounts reclassed from accumulated other comprehensive loss	2,394
Ending Balance	(9,062)	(15,993)
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(19,854)	(15,020)	(13,926)
Ending Balance	$ (8,479)	$ (19,854)	$ (15,020)

Business Combinations - Narrati

Business Combinations - Narrative (Details) - USD ($)	May 01, 2018	Mar. 31, 2020	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Consideration paid, net of cash acquired				$ 0	$ 0	$ 743,249,000
EPMH
Business Acquisition [Line Items]
Fair value of assets acquired			$ 902,547,000			905,875,000
Fair value of liabilities assumed			159,298,000			162,626,000
Decrease in inventory			0
Increase in accounts receivable			0
Decrease in property, plant, and equipment			$ 1,937,000
Consideration paid, net of cash acquired	$ 743,200,000
Cash acquired	19,100,000
Net working capital post-closing adjustments	$ 500,000
Revenues from acquiree included in Income Statement						158,800,000
Net loss from acquiree included in Income Statement						600,000
Non-recurring transaction costs attributable to business combination excluded from pro-forma information						179,220,000	$ (116,899,000)
EPMH | Acquisition-related Costs
Business Acquisition [Line Items]
Non-recurring transaction costs attributable to business combination excluded from pro-forma information						15,200,000
EPMH | Selling, general, and administrative
Business Acquisition [Line Items]
Acquisition-related costs						$ 13,600,000
Arrows Up LLC | SandBox Logistics
Business Acquisition [Line Items]
Consideration paid		$ 0
Fair value of assets acquired		20,100,000
Fair value of liabilities assumed		2,500,000
Gain on bargain purchase recognized		$ 17,600,000
Decrease in inventory				3,300,000
Increase in accounts receivable				1,000,000
Decrease in property, plant, and equipment				100,000
Adjustment to gain on bargain purchase initially recognized				$ 2,400,000

Business Combinations - Purchas

Business Combinations - Purchase Price Allocation (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Purchase Price
Goodwill		$ 185,649	$ 273,524	$ 261,340
EPMH
Purchase Price
Accounts receivable, net	$ 43,305			43,305
Inventories	86,112			86,112
Property, plant and mine development	146,558			148,495
Mineral rights	408,889			419,469
Identifiable intangible assets - finite lived	8,770			10,270
Identifiable intangible assets - indefinite lived	36,800			38,050
Prepaids and deposits	1,827			2,072
Other assets	7,474			7,474
Goodwill	162,812			150,628
Total assets acquired	902,547			905,875
Accounts payable	13,435			13,435
Accrued expenses and other current liabilities	10,304			10,304
Deferred tax liabilities	119,483			122,811
Long term obligations	16,076			16,076
Total liabilities assumed	159,298			162,626
Net assets acquired	743,249			$ 743,249
Measurement Period Adjustments
Accounts receivable, net	0
Inventories	0
Property, plant and mine development	(1,937)
Mineral rights	(10,580)
Identifiable intangible assets - finite lived	(1,500)
Identifiable intangible assets - indefinite lived	(1,250)
Prepaids and deposits	(245)
Other assets	0
Goodwill	12,184	$ (1,775)
Total assets acquired	(3,328)
Accounts payable	0
Accrued expenses and other current liabilities	0
Deferred tax liabilities	(3,328)
Long term obligations	0
Total liabilities assumed	(3,328)
Net assets acquired	$ 0

Business Combinations - Intangi

Business Combinations - Intangible Assets Acquired (Details) - EPMH - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Identifiable intangible assets - finite lived, Approximate Fair Value	$ 8,770	$ 10,270
Identifiable intangible assets - indefinite lived, Approximate Fair Value	36,800	$ 38,050
Trade names
Business Acquisition [Line Items]
Identifiable intangible assets - indefinite lived, Approximate Fair Value	36,800
Technology and intellectual property
Business Acquisition [Line Items]
Identifiable intangible assets - finite lived, Approximate Fair Value	$ 1,400
Identifiable intangible assets - finite lived, Estimated Useful Life (in years)	15 years
Customer relationships
Business Acquisition [Line Items]
Identifiable intangible assets - finite lived, Approximate Fair Value	$ 7,370
Identifiable intangible assets - finite lived, Estimated Useful Life (in years)	15 years

Business Combinations - Pro For

Business Combinations - Pro Forma Information (Details) - EPMH - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Sales	$ 1,659,775	$ 1,454,070
Net (loss) income	$ (179,220)	$ 116,899
Basic (loss) earnings per share (in dollars per share)	$ (2.34)	$ 1.44
Diluted (loss) earnings per share (in dollars per share)	$ (2.34)	$ 1.43

Accounts Receivable (Details)

Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Receivables [Abstract]
Trade receivables	$ 171,230	$ 178,182
Less: Provision for credit losses	(6,604)	(8,984)
Net trade receivables	164,626	169,198
Other receivables	42,308	13,040
Total accounts receivable	206,934	182,238
Net NOL carryback claims receivable under CARES Act	$ 37,400
Refundable alternative minimum tax credits		$ 8,100

Accounts Receivable - Allowance

Accounts Receivable - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts Receivable Roll Forward
Beginning balance, December 31, 2019	$ 8,984
Provision for credit losses	1,510	$ 3,466	$ 315
Write-offs	(3,890)
Ending balance, December 31, 2020	6,604	8,984
Oil & Gas Proppants
Allowance for Doubtful Accounts Receivable Roll Forward
Beginning balance, December 31, 2019	7,640
Provision for credit losses	1,340
Write-offs	(3,296)
Ending balance, December 31, 2020	5,684	7,640
Industrial & Specialty Products
Allowance for Doubtful Accounts Receivable Roll Forward
Beginning balance, December 31, 2019	1,344
Provision for credit losses	170
Write-offs	(594)
Ending balance, December 31, 2020	$ 920	$ 1,344

Accounts Receivable - Narrative

Accounts Receivable - Narrative (Details) - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Sales | Ten Largest Customers
Concentration Risk [Line Items]
Concentration risk percentage	34.00%	43.00%	48.00%
Sales | One Customer
Concentration Risk [Line Items]
Concentration risk percentage	24.00%	11.00%	15.00%
Trade Accounts Receivables | One Customer
Concentration Risk [Line Items]
Concentration risk percentage		12.00%

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Supplies	$ 42,329	$ 47,277
Raw materials and work in process	33,723	41,167
Finished goods	28,632	35,988
Total inventories	$ 104,684	$ 124,432

Property, Plant and Mine Deve_3

Property, Plant and Mine Development (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment
Property, plant and mine development, gross	$ 2,207,494	$ 2,224,197
Accumulated depletion, depreciation, amortization and impairment charges	(839,402)	(706,610)
Property, plant and mine development, net	1,368,092	1,517,587
Mining property and mine development
Property, Plant and Equipment
Property, plant and mine development, gross	788,287	794,899
Asset retirement cost
Property, Plant and Equipment
Property, plant and mine development, gross	15,985	18,260
Land
Property, Plant and Equipment
Property, plant and mine development, gross	54,710	57,082
Land improvements
Property, Plant and Equipment
Property, plant and mine development, gross	76,002	73,203
Buildings
Property, Plant and Equipment
Property, plant and mine development, gross	69,841	69,112
Machinery and equipment
Property, Plant and Equipment
Property, plant and mine development, gross	1,171,382	1,152,898
Furniture and fixtures
Property, Plant and Equipment
Property, plant and mine development, gross	4,071	4,068
Construction-in-progress
Property, Plant and Equipment
Property, plant and mine development, gross	$ 27,216	$ 54,675

Property, Plant and Mine Deve_4

Property, Plant and Mine Development - Narrative (Details)	Mar. 21, 2018USD ($)transload	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jun. 30, 2018USD ($)
Property, Plant and Equipment
Depreciation expense				$ 143,800,000	$ 168,600,000
Gain on sale of transload facilities				2,597,000	(1,573,000)	$ 5,170,000
Disposal Group, Held-for-sale, Not Discontinued Operations | Land
Property, Plant and Equipment
Impairment recognized on assets held for sale				0	0
Disposal Group, Held-for-sale, Not Discontinued Operations | Land | Prepaid expenses and other current assets
Property, Plant and Equipment
Assets held for sale		$ 3,200,000	$ 1,300,000	3,200,000	1,300,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Land
Property, Plant and Equipment
Gain on sale of assets		300,000	600,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Permian, Eagle Ford, and Appalachian Basins | CIG Logistics
Property, Plant and Equipment
Number of transload facilities sold | transload	3
Total consideration received on sale of transload facilities	$ 86,100,000
Liabilities assumed by buyer on sale of transload facilities	2,200,000
Cash consideration received on sale of transload facilities	83,900,000
Gain on sale of transload facilities	5,800,000
Consideration received allocated to asset retirement obligations liabilities of transload facilities	2,100,000
Equipment note assumed the buyer on sale of transload facilities	100,000
Consideration allocated to vendor incentives in sale of transload facilities	60,300,000
Accrued contract termination costs for facilities operated by third parties on sale of transload facilities	7,900,000
Settlement credit for contract termination costs on facilities operated by third parties on sale of transload facilities							$ 2,700,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Permian, Eagle Ford, and Appalachian Basins | CIG Logistics | Accounts payables and accrued liabilities
Property, Plant and Equipment
Consideration allocated to vendor incentives in sale of transload facilities		$ 4,800,000	$ 26,600,000	4,800,000	26,600,000
Plant and Mine Development
Property, Plant and Equipment
Interest cost capitalized in property, plant and mine development				$ 33,000	$ 2,000,000
Transload facilities | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Permian, Eagle Ford, and Appalachian Basins | CIG Logistics
Property, Plant and Equipment
Consideration received allocated to fair value of transload facilities	25,800,000
Net book value of transload facilities	$ 20,000,000

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2020	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Beginning balance	$ 273,524	$ 261,340	$ 273,524	$ 261,340
Impairment losses			(86,100)	0	$ (164,167)
Ending balance			185,649	273,524	261,340
EPMH
Goodwill [Roll Forward]
Beginning balance		150,628		150,628
Acquisition and measurement period adjustment				12,184
Acquisition adjustment		12,184	(1,775)
Ending balance		162,812			150,628
Oil & Gas Proppants
Goodwill [Roll Forward]
Beginning balance	86,100	86,100	86,100	86,100
Impairment losses			(86,100)
Ending balance			0	86,100	86,100
Oil & Gas Proppants | EPMH
Goodwill [Roll Forward]
Acquisition and measurement period adjustment				0
Acquisition adjustment			0
Industrial & Specialty Products
Goodwill [Roll Forward]
Beginning balance	187,424	$ 175,240	187,424	175,240
Impairment losses			0
Ending balance			185,649	187,424	$ 175,240
Industrial & Specialty Products | EPMH
Goodwill [Roll Forward]
Acquisition and measurement period adjustment				$ 12,184
Acquisition adjustment	$ 1,800		$ (1,775)

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Changes in the Carrying Amount of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets
Gross Carrying Amount	$ 138,051	$ 154,782
Accumulated Amortization	(42,036)	(35,817)
Impairments	(1,373)	(1,240)
Net	94,642	117,725
Total Intangible Assets
Gross Carrying Amount	204,141	220,872
Accumulated Amortization	(42,036)	(35,817)
Impairments	(2,523)	(1,240)
Intangible assets, net	159,582	183,815
Trade names
Indefinite-lived Intangible Assets
Gross Carrying Amount	65,390	65,390
Impairments	(1,150)	0
Net	64,240	65,390
Other
Indefinite-lived Intangible Assets
Gross Carrying Amount	700	700
Impairments	0	0
Net	700	700
Technology and intellectual property
Finite-Lived Intangible Assets
Gross Carrying Amount	71,052	86,183
Accumulated Amortization	(18,854)	(17,080)
Impairments	(1,373)	0
Net	50,825	69,103
Total Intangible Assets
Accumulated Amortization	(18,854)	(17,080)
Customer relationships
Finite-Lived Intangible Assets
Gross Carrying Amount	66,999	68,599
Accumulated Amortization	(23,182)	(18,737)
Impairments	0	(1,240)
Net	43,817	48,622
Total Intangible Assets
Accumulated Amortization	$ (23,182)	$ (18,737)

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Narrative (Details) - USD ($)	3 Months Ended			6 Months Ended	12 Months Ended
	Jun. 30, 2020	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill impairment					$ 86,100,000	$ 0	$ 164,167,000
Amortization expense					$ 10,300,000	10,800,000	$ 9,700,000
EPMH
Acquired Finite-Lived Intangible Assets [Line Items]
Decrease in technology intangibles				$ 1,500,000
Decrease in intellectual property intangibles				$ 1,250,000
Technology and intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful live of finite-lived intangible assets					15 years
Technology and intellectual property | EPMH
Acquired Finite-Lived Intangible Assets [Line Items]
Decrease in technology intangibles		$ 1,500,000
Trade names | EPMH
Acquired Finite-Lived Intangible Assets [Line Items]
Decrease in intellectual property intangibles		$ 1,300,000
Oil & Gas Proppants
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill impairment					$ 86,100,000
Capitalized legal fees related to unsuccessful defense of patents	$ 11,800,000
Oil & Gas Proppants
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill impairment			$ 164,200,000		$ 86,100,000	$ 0
Maximum | Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful live of finite-lived intangible assets					20 years
Minimum | Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful live of finite-lived intangible assets					13 years

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets - Estimated Amortization Expense Related to Definite-Lived Intangible Assets (Details) $ in Thousands	Dec. 31, 2020USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2021	$ 9,623
2022	9,608
2023	9,603
2024	9,605
2025	$ 9,603

Accounts Payable and Accrued _3

Accounts Payable and Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Trade payables	$ 90,564	$ 181,029
Accrued salaries and wages	7,432	12,385
Accrued vacation liability	2,499	3,053
Current portion of liability for pension and post-retirement benefits	1,338	2,993
Accrued healthcare liability	1,886	4,078
Accrued property taxes and sales taxes	5,136	4,070
Vendor incentives	4,782	26,617
Other accrued liabilities	8,283	14,012
Accounts payable and accrued liabilities	$ 121,920	$ 248,237

Debt (Details)

Debt (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility
Less: Unamortized original issue discount	$ (4,376,000)	$ (5,412,000)
Less: Unamortized debt issuance cost	(20,259,000)	(25,390,000)
Finance leases	350,000	70,000
Total debt	1,239,702,000	1,232,448,000
Less: current portion	(42,042,000)	(18,463,000)
Total long-term portion of debt	1,197,660,000	1,213,985,000
Notes Payable | Insurance financing notes payable
Line of Credit Facility
Short-term debt	4,187,000	5,055,000
Notes Payable | Note payable secured by royalty interest
Line of Credit Facility
Long-term debt	0	10,438,000
Notes Payable | Equipment notes payable
Line of Credit Facility
Long-term debt	$ 0	$ 87,000
Revolving Credit Facility | Revolver expiring May 1, 2023 (4.19% at December 31, 2020 and 7.75% at December 31, 2019)
Line of Credit Facility
Credit facility, interest rate	4.19%	7.75%
Long-term debt	$ 25,000,000	$ 0
Senior Secured Credit Facility | Term Loan facility—final maturity May 1, 2025 (5.00% at December 31, 2020 and 5.81% December 31, 2019)
Line of Credit Facility
Credit facility, interest rate	5.00%	5.81%
Long-term debt	$ 1,234,800,000	$ 1,247,600,000

Debt - Narrative (Details)

Debt - Narrative (Details)	May 01, 2018USD ($)	Dec. 31, 2020USD ($)payment	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)payment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Aug. 16, 2016USD ($)
Debt Instrument [Line Items]
Gain recorded due to changes in fair value of debt				$ 8,263,000	$ 16,854,000	$ 0
Insurance financing notes payable | Notes Payable
Debt Instrument [Line Items]
Debt stated interest rate			3.00%
Debt term			9 months
Notes payable balance		$ 4,187,000		4,187,000	5,055,000
Senior Secured Credit Facility | Term Loan
Debt Instrument [Line Items]
Credit facility consolidated total net leverage ratio	3.75
Debt repurchased			$ 10,000,000
Debt redemption price percentage			95.50%
Debt issuance costs			$ 400,000
Gain on extinguishment of debt			$ 100,000
Senior Secured Credit Facility | Revolver
Debt Instrument [Line Items]
Net leverage ratio, credit facility threshold percentage	30.00%
Revolving Credit Facility | Revolver
Debt Instrument [Line Items]
Available borrowing base		100,000,000		100,000,000
Amount drawn under credit facility		25,000,000		25,000,000
Amount available under credit facility		52,000,000		52,000,000
Letter of Credit | Revolver
Debt Instrument [Line Items]
Amount allocated for letters of credit		$ 23,000,000		$ 23,000,000
Current consolidated leverage ratio		6.07		6.07
Current borrowing capacity under credit facility without consent of lenders		$ 30,000,000		$ 30,000,000
Senior Secured Credit Facility
Debt Instrument [Line Items]
Debt issued	$ 1,380,000,000
Senior Secured Credit Facility | Term Loan
Debt Instrument [Line Items]
Debt issued	1,280,000,000
Senior Secured Credit Facility | Revolving Credit Facility | Revolver
Debt Instrument [Line Items]
Available borrowing base	100,000,000
Capitalized debt issuance costs	$ 38,700,000
Notes Payable | Note payable secured by royalty interest
Debt Instrument [Line Items]
Gain on extinguishment of debt		$ 8,300,000
Debt fair value							$ 22,500,000
Number of debt settlement payments | payment		1		1
Debt settlement		$ 2,550,000
Accrued royalties		$ 0		$ 0
Gain recorded due to changes in fair value of debt					$ 16,900,000
Notes Payable | Note payable secured by royalty interest | Measurement Input, Discount Rate
Debt Instrument [Line Items]
Fair value discount rate							0.14

Debt - Contractual Maturities o

Debt - Contractual Maturities of Senior Secured Credit Facility (Details) - Senior Secured Credit Facility - Term Loan - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
2021	$ 12,800
2022	12,800
2023	12,800
2024	12,800
2025	1,183,600
Thereafter	0
Total	$ 1,234,800	$ 1,247,600

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]
Other long-term liabilities related to asset retirement obligation	$ 24,700	$ 25,800
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	25,825	18,413
Accretion	1,434	1,531
Additions and revisions of estimates	(2,542)	5,881
Ending balance	$ 24,717	$ 25,825

Fair Value Accounting (Details)

Fair Value Accounting (Details)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)derivative
Interest Rate Swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivative number of instruments held | derivative		2
Fair value of derivatives	$ 0
Notes Payable | Note payable secured by royalty interest
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Note payable balance	$ 0	$ 10,438,000

Derivative Instruments - Estima

Derivative Instruments - Estimated Fair Values of Derivative Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Interest rate swap agreement $400 million
Derivative Instruments, Gain (Loss)
Contract/Notional Amount	$ 440,000	$ 440,000
Carrying Amount	0	(2,768)
Fair Value	0	$ (2,768)
Interest rate swap agreement $400 million | LIBOR
Derivative Instruments, Gain (Loss)
Derivative interest rate base		2.74%
Interest rate swap agreement $200 million
Derivative Instruments, Gain (Loss)
Contract/Notional Amount	200,000	$ 200,000
Carrying Amount	0	(1,259)
Fair Value	$ 0	$ (1,259)
Interest rate swap agreement $200 million | LIBOR
Derivative Instruments, Gain (Loss)
Derivative interest rate base		2.74%

Derivative Instruments - Narrat

Derivative Instruments - Narrative (Details)	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)derivative
Interest Rate Swap
Derivative [Line Items]
Fair value of derivatives	$ 0
Derivative number of instruments held | derivative		2
Ineffectiveness of derivatives	0
Interest Rate Swap | Other long-term obligations | Cash Flow Hedges
Derivative [Line Items]
Fair value of derivatives	0
Derivative number of instruments held | derivative		2
Interest rate swap agreement $400 million
Derivative [Line Items]
Fair value of derivatives	0	$ 2,768,000
Interest rate swap agreement $400 million | Other long-term obligations | Cash Flow Hedges
Derivative [Line Items]
Fair value of derivatives		2,800,000
Interest rate swap agreement $200 million
Derivative [Line Items]
Fair value of derivatives	$ 0	1,259,000
Interest rate swap agreement $200 million | Other long-term obligations | Cash Flow Hedges
Derivative [Line Items]
Fair value of derivatives		1,300,000
Interest rate cap agreement
Derivative [Line Items]
Deferred losses reclassified from accumulated other comprehensive income into earnings related to interest rate swap derivatives not longer qualifying as hedging		$ 76,000

Derivative Instruments - Effect

Derivative Instruments - Effect of Derivatives Instruments on Combined Statements of Operations and Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ 716,580	$ 1,052,304	$ 1,396,506
Gain (loss) recognized in OCI from derivative instruments	8,981
Ending Balance	626,791	716,580	1,052,304
Unrealized income (loss) on cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(3,053)	(1,621)	(76)
Gain (loss) recognized in OCI from derivative instruments	3,053	(1,432)	(1,622)
Loss reclassified from Accumulated OCI	0	0	77
Ending Balance	$ 0	$ (3,053)	$ (1,621)

Equity-Based Compensation - Nar

Equity-Based Compensation - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	0	0	0
Stock options exercised (in shares)	0	10,000	4,167
Intrinsic value of stock options exercised	$ 0	$ 12,000	$ 100,000
Proceeds from options exercised	0	128,000	61,000
Tax benefit realized from stock options exercised	0	3,000	14,000
Unrecognized compensation expense related to stock options	0	0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized equity-based compensation		1,400,000
Restricted Stock and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized equity-based compensation	$ 8,100,000	$ 8,200,000	$ 7,600,000
Awards share units granted (in shares)	1,590,170	814,387	415,110
Unrecognized compensation expense related to awards	$ 6,600,000
Recognized weighted-average period	1 year 7 months 6 days
Vesting period for awards of equity instruments	3 years
Grant date fair value of awards granted (in dollars per share)	$ 4.09
Restricted Stock and Restricted Stock Units to be Settled in Cash
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized equity-based compensation	$ 600,000
Awards share units granted (in shares)	335,039
Unrecognized compensation expense related to awards	$ 1,400,000
Recognized weighted-average period	2 years 1 month 6 days
Awards forfeited and partially vested (in shares)	58,246
Vesting period for awards of equity instruments	3 years
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized equity-based compensation	$ 6,800,000	$ 7,700,000	$ 13,300,000
Awards share units granted (in shares)	1,020,161	607,130	261,500
Unrecognized compensation expense related to awards	$ 6,100,000
Recognized weighted-average period	1 year 8 months 12 days
Vesting period for awards of equity instruments	3 years
Grant date fair value of awards granted (in dollars per share)	$ 6.57	$ 15.58	$ 31.24
Performance Shares to be Settled in Cash
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized equity-based compensation	$ 900,000
Unrecognized compensation expense related to awards	$ 1,300,000
Recognized weighted-average period	2 years 1 month 6 days
Vesting period for awards of equity instruments	3 years
2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock that may be issued (in shares)	3,752,317

Equity-Based Compensation - Sto

Equity-Based Compensation - Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Outstanding at December 31, 2019 (in shares)	826,658
Granted (in shares)	0	0	0
Exercised (in shares)	0	(10,000)	(4,167)
Forfeited (in shares)	(443)
Expired (in shares)	0
Outstanding at December 31, 2020 (in shares)	826,215	826,658
Exercisable at December 31, 2020 (in shares)	826,215
Weighted Average Exercise Price
Outstanding at December 31, 2019, (in dollars per share)	$ 28.97
Granted (in dollars per share)	0
Exercised (in dollars per share)	0
Forfeited (in dollars per share)	32.41
Expired (in dollars per share)	0
Outstanding at December 31, 2020, (in dollars per share)	29.05	$ 28.97
Exercisable at December 31, 2020 (in dollars per share)	$ 29.05
Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2020	$ 0	$ 11,557
Exercisable at December 31, 2020	$ 0
Weighted Average Remaining Contractual Term in Years
Outstanding at December 31, 2020	3 years 1 month 6 days	4 years 1 month 6 days
Exercisable at December 31, 2020	3 years 1 month 6 days

Equity-Based Compensation - Res

Equity-Based Compensation - Restricted Stock and Restricted Stock Units Activity (Details) - Restricted Stock and Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Unvested, December 31, 2019 (in shares)	1,020,248
Granted (in shares)	1,590,170	814,387	415,110
Vested (in shares)	(539,614)
Forfeited (in shares)	(290,978)
Unvested, December 31, 2020 (in shares)	1,779,826	1,020,248
Grant Date Weighted Average Fair Value
Unvested, December 31, 2019 (in dollars per share)	$ 15.86
Granted (in dollars per share)	4.09
Vested (in dollars per share)	15.98
Forfeited (in dollars per share)	10.66
Unvested, December 31, 2020 (in dollars per share)	$ 6.22	$ 15.86

Equity-Based Compensation - Per

Equity-Based Compensation - Performance Share Unit Activity (Details) - Performance Share Units - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Unvested, December 31, 2019 (in shares)	838,722
Granted (in shares)	1,020,161	607,130	261,500
Vested (in shares)	0
Forfeited/Canceled (in shares)	(345,235)
Unvested, December 31, 2020 (in shares)	1,513,648	838,722
Weighted Average
Unvested, December 31, 2019 (in dollars per share)	$ 18
Granted (in dollars per share)	6.57	$ 15.58	$ 31.24
Vested (in dollars per share)	0
Forfeited/Canceled (in dollars per share)	24.23
Unvested, December 31, 2020 (in dollars per share)	$ 12.36	$ 18

Commitments and Contingencies -

Commitments and Contingencies - Future Minimum Annual Commitments (Details) $ in Thousands	Dec. 31, 2020USD ($)
Minimum Purchase Commitments
2021	$ 14,812
2022	10,328
2023	10,328
2024	7,020
2025	2,654
Thereafter	6,604
Total future purchase commitments	$ 51,746

Commitments and Contingencies_2

Commitments and Contingencies - Narrative (Details)	May 17, 2017USD ($)	Dec. 31, 2020USD ($)claim	Dec. 31, 2019USD ($)claim	Dec. 31, 2018claim
Loss Contingencies
Purchased reserves	$ 94,400,000
Surety Bonds
Loss Contingencies
Surety bonds outstanding		$ 35,100,000
Reclamation Bonds
Loss Contingencies
Surety bonds outstanding		31,100,000
Other non-current assets
Loss Contingencies
Third party products claims liability under insurance in other long-term obligations		0	$ 0
Other long-term obligations
Loss Contingencies
Third party products claims liability under insurance in other long-term obligations		$ 1,000,000	$ 900,000
Pending Litigation
Loss Contingencies
Number of new claims filed | claim		1	1	20
Number of pending claims | claim		52

Pension and Post-Retirement B_3

Pension and Post-Retirement Benefits - Net Pension Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Pension Plans, Postretirement and Other Employee Benefits
Service cost	$ 2,253	$ 1,304	$ 1,307
Interest cost	4,037	5,375	4,632
Expected return on plan assets	(6,019)	(6,171)	(5,969)
Net amortization and deferral	3,127	1,648	2,526
Net pension benefit or post-retirement costs	3,398	2,156	2,496
Post-retirement Benefits
Pension Plans, Postretirement and Other Employee Benefits
Service cost	70	88	102
Interest cost	584	789	740
Unrecognized net (gain)/loss	0	(29)	0
Net pension benefit or post-retirement costs	$ 654	$ 848	$ 842

Pension and Post-Retirement B_4

Pension and Post-Retirement Benefits - Changes in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Plan Assets
Fair value of plan assets at January 1,	$ 110,431
Fair value of plan assets at December 31,	120,563	$ 110,431
Pension Benefits
Benefit Obligation
Benefit obligation at January 1,	148,491	138,900
Service cost	2,253	1,304	$ 1,307
Interest cost	4,037	5,375	4,632
Actuarial (gain) loss	11,119	17,225
Benefits paid	(8,649)	(14,922)
Other	(53)	609
Benefit obligation at December 31,	157,198	148,491	138,900
Plan Assets
Fair value of plan assets at January 1,	110,431	102,396
Actual return on plan assets	13,306	17,919
Employer contributions	5,475	4,755
Benefits paid	(8,649)	(14,922)
Other	0	283
Fair value of plan assets at December 31,	120,563	110,431	102,396
Plan assets less than benefit obligations at December 31 recognized as liability for pension and other post-retirement benefits	(36,635)	(38,060)
Post-retirement Benefits
Benefit Obligation
Benefit obligation at January 1,	22,054	21,570
Service cost	70	88	102
Interest cost	584	789	740
Actuarial (gain) loss	1,329	206
Benefits paid	(1,751)	(815)
Other	(10,968)	216
Benefit obligation at December 31,	11,318	22,054	21,570
Plan Assets
Fair value of plan assets at January 1,	0	0
Actual return on plan assets	0	0
Employer contributions	1,335	599
Benefits paid	(1,751)	(815)
Other	416	216
Fair value of plan assets at December 31,	0	0	$ 0
Plan assets less than benefit obligations at December 31 recognized as liability for pension and other post-retirement benefits	$ (11,318)	$ (22,054)

Pension and Post-Retirement B_5

Pension and Post-Retirement Benefits - Narrative (Details)	12 Months Ended
	Dec. 31, 2020USD ($)plan	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Pension Plans, Postretirement and Other Employee Benefits
Projected benefit obligation, nonqualified pension plan	$ 1,600,000	$ 1,600,000
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate accumulated benefit obligation	1,600,000	1,600,000
Fair value of plan assets, nonqualified pension plan	0	0
Defined benefit plan, accumulated other comprehensive income net gains (losses), after tax	24,700,000	22,100,000
Total amounts in accumulated other comprehensive (loss) income	$ (9,400,000)	$ 2,200,000
Number of multiemployer defined benefit plans | plan	3
Percentage of contributions to individual multiemployer funds	5.00%	5.00%	5.00%
Company contributions to defined contribution plan	$ 3,500,000	$ 6,100,000	$ 2,600,000
Certain Employees
Pension Plans, Postretirement and Other Employee Benefits
Company contribution over defined benefit plan	4.00%
All Eligible Employees
Pension Plans, Postretirement and Other Employee Benefits
Company contribution over defined benefit plan	6.00%
Pension Benefits
Pension Plans, Postretirement and Other Employee Benefits
Accumulated benefit obligation	$ 157,200,000	$ 148,500,000
Expected contributions to the plans for next fiscal year	5,300,000
Post-retirement Benefits
Pension Plans, Postretirement and Other Employee Benefits
Expected contributions to the plans for next fiscal year	$ 1,200,000

Pension and Post-Retirement B_6

Pension and Post-Retirement Benefits - Estimated Future Pension and Post-Retirement Benefit Payments (Details) $ in Thousands	Dec. 31, 2020USD ($)
Pension Benefits
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021	$ 9,329
2022	9,346
2023	9,326
2024	9,678
2025	9,224
2026-2030	44,832
Post-retirement Benefits | Before Medicare Subsidy
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021	1,217
2022	1,095
2023	1,002
2024	959
2025	883
2026-2030	3,393
Post-retirement Benefits | After Medicare Subsidy
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021	1,217
2022	1,095
2023	1,002
2024	959
2025	883
2026-2030	$ 3,393

Pension and Post-Retirement B_7

Pension and Post-Retirement Benefits - Weighted-Average Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Pension Plans, Postretirement and Other Employee Benefits
Discount rate	2.50%	3.20%
Long-term rate of compensation increase	3.00%
Long-term rate of return on plan assets	6.30%	6.30%
Pension Benefits | Minimum
Pension Plans, Postretirement and Other Employee Benefits
Long-term rate of compensation increase		3.00%
Pension Benefits | Maximum
Pension Plans, Postretirement and Other Employee Benefits
Long-term rate of compensation increase		3.50%
Post-retirement Benefits
Pension Plans, Postretirement and Other Employee Benefits
Discount rate	2.10%	3.20%
Post-retirement Benefits | Pre-65
Pension Plans, Postretirement and Other Employee Benefits
Initial rate	6.50%	7.00%
Ultimate rate	4.50%	4.50%
Post-retirement Benefits | Post-65
Pension Plans, Postretirement and Other Employee Benefits
Initial rate	7.00%	7.50%
Ultimate rate	4.50%	4.50%

Pension and Post-Retirement B_8

Pension and Post-Retirement Benefits - Investment Categories and Their Relative Percentage of Fair Value to Total Plan Assets (Details)	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits | Equity securities
Pension Plans, Postretirement and Other Employee Benefits
Percentage of the fair value of the total plan assets	57.90%	52.10%
Pension Benefits | Debt securities
Pension Plans, Postretirement and Other Employee Benefits
Percentage of the fair value of the total plan assets	41.30%	46.60%
Pension Benefits | Cash
Pension Plans, Postretirement and Other Employee Benefits
Percentage of the fair value of the total plan assets	0.80%	1.30%
Post-retirement Benefits | Equity securities
Pension Plans, Postretirement and Other Employee Benefits
Percentage of the fair value of the total plan assets	0.00%	0.00%
Post-retirement Benefits | Debt securities
Pension Plans, Postretirement and Other Employee Benefits
Percentage of the fair value of the total plan assets	0.00%	0.00%
Post-retirement Benefits | Cash
Pension Plans, Postretirement and Other Employee Benefits
Percentage of the fair value of the total plan assets	0.00%	0.00%

Pension and Post-Retirement B_9

Pension and Post-Retirement Benefits - Fair Value of Pension Plan Assets, by Asset Category (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	$ 120,563	$ 110,431
Cash and cash equivalents
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	1,020	1,385
Diversified emerging markets
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	7,064	4,942
Foreign large blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	22,638	19,183
Large-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	22,272	20,738
Mid-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	12,972	8,416
Real estate
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	4,822	4,309
Corporate notes and bonds
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	38,983	37,664
U.S. Treasuries
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	8,582	10,894
Mortgage-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	1,780	2,496
Asset-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	430	404
Level 1
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	117,333	106,146
Level 1 | Cash and cash equivalents
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 1 | Diversified emerging markets
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	7,064	4,942
Level 1 | Foreign large blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	22,638	19,183
Level 1 | Large-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	22,272	20,738
Level 1 | Mid-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	12,972	8,416
Level 1 | Real estate
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	4,822	4,309
Level 1 | Corporate notes and bonds
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	38,983	37,664
Level 1 | U.S. Treasuries
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	8,582	10,894
Level 1 | Mortgage-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 1 | Asset-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	3,230	4,285
Level 2 | Cash and cash equivalents
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	1,020	1,385
Level 2 | Diversified emerging markets
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Foreign large blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Large-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Mid-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Real estate
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Corporate notes and bonds
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | U.S. Treasuries
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 2 | Mortgage-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	1,780	2,496
Level 2 | Asset-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	430	404
Level 3
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Cash and cash equivalents
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Diversified emerging markets
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Foreign large blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Large-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Mid-cap blend
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Real estate
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Corporate notes and bonds
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | U.S. Treasuries
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Mortgage-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	0	0
Level 3 | Asset-backed securities
Pension Plans, Postretirement and Other Employee Benefits
Fair value of pension plan assets	$ 0	$ 0

Pension and Post-Retirement _10

Pension and Post-Retirement Benefits - Summary of Multiemployer Pension Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
LIUNA
Pension Plans, Postretirement and Other Employee Benefits
EIN/ Pension Plan No.	52-6074345/001
Company Contributions (in thousands)	$ 361	$ 385	$ 573
Expiration Date of CBA	Jun. 4, 2022
IUOE
Pension Plans, Postretirement and Other Employee Benefits
EIN/ Pension Plan No.	36-6052390/001
Company Contributions (in thousands)	$ 256	310	1,385
Expiration Date of CBA	Jul. 31, 2022
CSSS
Pension Plans, Postretirement and Other Employee Benefits
EIN/ Pension Plan No.	36-6044243/001
Company Contributions (in thousands)	$ 51	$ 51	$ 51
Central States, Southeast and Southwest Areas Pension Plan
Pension Plans, Postretirement and Other Employee Benefits
Withdrawal liability from pension plan	1,000
Withdrawal liability paid in monthly installments	$ 4

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Gain on lease concessions	$ 24,056	$ 0	$ 0
COVID 19
Lessee, Lease, Description [Line Items]
Decrease to ROU due to lease concessions	1,000
Decrease to lease liabilities due to lease concessions	25,000
Gain on lease concessions	$ 24,000
Minimum
Lessee, Lease, Description [Line Items]
Remaining term of lease contracts	1 year
Maximum
Lessee, Lease, Description [Line Items]
Remaining term of lease contracts	20 years

Leases - Supplemental Balance S

Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Operating	$ 37,469	$ 53,098
Finance	339	0
Total leased assets	37,808	53,098
Current
Operating	17,388	53,587
Finance	55	0
Non-Current
Operating	76,361	117,964
Finance	295	0
Total lease liabilities	$ 94,099	$ 171,551
Weighted average remaining lease term:
Operating leases	6 years 10 months 24 days	4 years 6 months
Finance leases	2 years 10 months 24 days
Weighted average discount rate:
Operating leases	5.80%	5.70%
Finance leases	5.00%	0.00%
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtCurrent	us-gaap:LongTermDebtCurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtNoncurrent	us-gaap:LongTermDebtNoncurrent

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Total lease costs	$ 31,762	$ 208,402
Finance lease expense	12
Cost of Sales
Lessee, Lease, Description [Line Items]
Operating lease costs	26,548	88,966
Short-term operating lease costs	9,600	18,200
Selling, general, and administrative
Lessee, Lease, Description [Line Items]
Operating lease costs	1,808	3,993
Short-term operating lease costs	400	700
Goodwill and other asset impairments
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 3,406	$ 115,443

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows for operating leases	$ 62,140	$ 74,740
Operating cash flows for finance leases	12	0
Right-of-use assets obtained in exchange for new lease liabilities:
Operating leases	10,747	232,123
Finance leases	$ 359	$ 0

Leases - Maturities of Lease Li

Leases - Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating leases
2021	$ 23,217
2022	16,447
2023	16,019
2024	14,181
2025	11,617
Thereafter	38,205
Total lease payments	119,686
Less: Interest	20,984
Less: Other operating expenses	4,953
Total	93,749
Finance leases
2021	71
2022	71
2023	244
2024	0
2025	0
Thereafter	0
Total lease payments	386
Less: Interest	36
Less: Other operating expenses	0
Total	$ 350	$ 70

Income Taxes - Income Tax Benef

Income Taxes - Income Tax Benefit (Expense) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal									$ 0	$ 0	$ 1,076
State									(307)	(1,188)	(2,496)
Foreign									(1,473)	(1,343)	(518)
Current income tax (expense) benefit									(1,780)	(2,531)	(1,938)
Deferred:
Federal									57,214	90,457	25,578
State									4,591	11,225	5,492
Foreign									0	0	0
Deferred income tax (expense) benefit									61,805	101,682	31,070
Income tax benefit	$ (3,760)	$ 4,094	$ 23,605	$ 36,086	$ 91,892	$ 7,671	$ (2,384)	$ 1,972	$ 60,025	$ 99,151	$ 29,132

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate on Pretax Earnings (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax (expense) benefit computed at U.S. federal statutory rate									$ 36,781	$ 90,070	$ 48,290
Decrease (increase) resulting from:
Statutory depletion									1,230	4,679	12,090
Goodwill impairment									0	0	(29,157)
Prior year tax return reconciliation									(2,084)	3,121	530
State income taxes, net of federal benefit									5,013	9,486	2,592
Adjustment to deferred taxes from the CARES Act									22,318	0	0
Equity compensation									(1,477)	(6,440)	(653)
Other, net									(1,756)	(1,765)	(4,560)
Income tax benefit	$ (3,760)	$ 4,094	$ 23,605	$ 36,086	$ 91,892	$ 7,671	$ (2,384)	$ 1,972	$ 60,025	$ 99,151	$ 29,132

Income Taxes - Tax Effects on D

Income Taxes - Tax Effects on Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Gross deferred tax assets:
Net operating loss carry forward and state tax credits	$ 90,087	$ 32,173
Pension and post-retirement benefit costs	11,146	13,976
Alternative minimum tax credit carry forward	0	7,895
Property, plant and equipment	6,866	7,179
Accrued expenses	12,397	15,336
Inventories	121	6,507
Federal tax credits	4,188	0
Stock-based compensation expense	4,307	2,390
Interest expense limitation	14,127	22,324
Intangibles	11,304	0
Lease obligation liability	14,154	29,604
Other	5,286	5,536
Total deferred tax assets	173,983	142,920
Gross deferred tax liabilities:
Land and mineral property basis difference	(122,265)	(124,182)
Fixed assets and depreciation	(100,640)	(44,314)
Intangibles	0	(12,541)
Other	(464)	(468)
Total deferred tax liabilities	(223,369)	(181,505)
Net deferred tax liabilities	$ (49,386)	$ (38,585)

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
General business credits	$ 4,188	$ 4,188		$ 0
Alternative minimum tax credit carry forward	16,000	16,000		$ 16,200
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	377,100	377,100
COVID 19
Operating Loss Carryforwards [Line Items]
Income tax refunds received		36,600
Refundable NOL credit under CARES Act	21,400	21,400	$ 26,300
Refunds received from NOL credits under CARES Act	4,900
Deferred tax benefit recorded under CARES Act		22,300
Refundable ATM credits under CARES Act	16,000	16,000
Deferred tax assets related to payroll taxes under CARES Act	$ 1,200	$ 1,200

Revenue - Sales by Major Source

Revenue - Sales by Major Source (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total Sales									$ 845,885	$ 1,474,477	$ 1,577,298
Oil & Gas Proppants
Disaggregation of Revenue [Line Items]
Total Sales									414,897	1,010,521
Industrial & Specialty Products
Disaggregation of Revenue [Line Items]
Total Sales									430,988	463,956
Product
Disaggregation of Revenue [Line Items]
Total Sales	$ 190,189	$ 159,637	$ 160,200	$ 222,161	$ 280,594	$ 287,977	$ 303,041	$ 296,860	732,187	1,168,472	1,282,799
Product | Oil & Gas Proppants
Disaggregation of Revenue [Line Items]
Total Sales									301,199	704,516
Product | Industrial & Specialty Products
Disaggregation of Revenue [Line Items]
Total Sales									430,988	463,956
Service
Disaggregation of Revenue [Line Items]
Total Sales	$ 37,088	$ 16,835	$ 12,337	$ 47,438	$ 58,465	$ 73,837	$ 91,813	$ 81,890	113,698	306,005	$ 294,499
Service | Oil & Gas Proppants
Disaggregation of Revenue [Line Items]
Total Sales									113,698	306,005
Service | Industrial & Specialty Products
Disaggregation of Revenue [Line Items]
Total Sales									$ 0	$ 0

Revenue - Changes in Contract A

Revenue - Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Unbilled Receivables
Beginning Balance	$ 20,144	$ 90
Reclassifications to billed receivables	(10,330)	(3,983)
Revenues recognized in excess of period billings	38,168	24,037
Ending Balance	47,982	20,144
Deferred Revenue
Beginning Balance	50,634	113,319
Revenues recognized from balances held at the beginning of the period	(19,704)	(65,225)
Revenues deferred from period collections on unfulfilled performance obligations	6,627	12,225
Revenues recognized from period collections	(3,865)	(9,685)
Ending Balance	$ 33,692	$ 50,634

Revenue - Narrative (Details)

Revenue - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Recognized revenue as variable consideration from shortfall penalties according to contract terms From Shortfall Penalties	$ 48	$ 70.6
Minimum | Supply Agreement
Disaggregation of Revenue [Line Items]
Deferred revenue, average initial contract term	1 year
Maximum | Supply Agreement
Disaggregation of Revenue [Line Items]
Deferred revenue, average initial contract term	15 years

Revenue - Remaining Performance

Revenue - Remaining Performance Obligation (Details)	Dec. 31, 2020
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining duration period of expected satisfaction of performance obligations	1 year

Revenue - Foreign Operations (D

Revenue - Foreign Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total sales									$ 845,885	$ 1,474,477	$ 1,577,298
Pre-tax income	$ 8,077	$ (18,310)	$ (56,223)	$ (108,691)	$ (385,317)	$ (30,736)	$ 8,445	$ (21,300)	(175,147)	(428,908)	(229,953)
Net income	4,567	$ (13,962)	$ (32,354)	$ (72,345)	(292,871)	$ (23,037)	$ 6,150	$ (19,324)	(114,094)	(329,082)	(200,808)
Consolidated assets	2,246,947				2,553,234				2,246,947	2,553,234
Foreign Operations
Disaggregation of Revenue [Line Items]
Total sales									86,179	92,788	66,917
Pre-tax income									8,509	7,010	5,901
Net income									6,722	5,538	$ 4,662
Consolidated assets	$ 31,000				$ 27,700				$ 31,000	$ 27,700

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Related party purchases	$ 0	$ 0	$ 2,958,000
Officer | Transportation Brokerage and Logistics Services Vendor
Related Party Transaction [Line Items]
Related party purchases	$ 0	$ 0	$ 2,900,000

Segment Reporting - Narrative (

Segment Reporting - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)SegmentProduct	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Segment Reporting Information
Number of reportable segments | Segment	2
Number of product types | Product	400
Goodwill	$ 185,649	$ 273,524	$ 261,340
Oil & Gas Proppants
Segment Reporting Information
Goodwill	0	86,100	86,100
Industrial & Specialty Products
Segment Reporting Information
Goodwill	185,649	187,424	$ 175,240
Operating Segments | Oil & Gas Proppants
Segment Reporting Information
Goodwill	0	86,100
Operating Segments | Industrial & Specialty Products
Segment Reporting Information
Goodwill	$ 185,600	$ 187,400

Segment Reporting - Sales and S

Segment Reporting - Sales and Segment Contribution Margin for Reporting Segments and Other Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information
Total sales									$ 845,885	$ 1,474,477	$ 1,577,298
Selling, general and administrative	$ (27,777)	$ (27,216)	$ (39,126)	$ (30,052)	$ (37,325)	$ (40,208)	$ (38,659)	$ (34,656)	(124,171)	(150,848)	(146,971)
Depreciation, depletion and amortization	(39,964)	(40,069)	(37,086)	(38,449)	(42,819)	(47,126)	(44,899)	(44,600)	(155,568)	(179,444)	(148,832)
Goodwill and other asset impairments	(2,644)	(222)	(3,956)	(103,866)	(363,717)	(130)	0	0	(110,688)	(363,847)	(281,899)
Interest expense	(16,155)	(19,274)	(22,179)	(22,277)	(22,996)	(24,733)	(23,765)	(23,978)	(79,885)	(95,472)	(70,564)
Other income (expense), net, including interest income	8,758	(409)	(1,670)	17,671	443	3,280	15,074	722	24,350	19,519	4,144
Income tax benefit	(3,760)	4,094	23,605	36,086	91,892	7,671	(2,384)	1,972	60,025	99,151	29,132
Net loss	4,317	(14,216)	(32,618)	(72,605)	(293,425)	(23,065)	6,061	(19,328)	(115,122)	(329,757)	(200,821)
Less: Net loss attributable to non-controlling interest	(250)	(254)	(264)	(260)	(554)	(28)	(89)	(4)	(1,028)	(675)	(13)
Net loss attributable to U.S. Silica Holdings, Inc.	$ 4,567	$ (13,962)	$ (32,354)	$ (72,345)	$ (292,871)	$ (23,037)	$ 6,150	$ (19,324)	(114,094)	(329,082)	(200,808)
Operating Segments
Segment Reporting Information
Total sales									845,885	1,474,477	1,577,298
Total segment contribution margin									301,217	426,809	512,930
Segment Reconciling Items
Segment Reporting Information
Operating activities excluded from segment cost of sales									(30,402)	(85,625)	(98,761)
Selling, general and administrative									(124,171)	(150,848)	(146,971)
Depreciation, depletion and amortization									(155,568)	(179,444)	(148,832)
Goodwill and other asset impairments									(110,688)	(363,847)	(281,899)
Interest expense									(79,885)	(95,472)	(70,564)
Other income (expense), net, including interest income									24,350	19,519	4,144
Oil & Gas Proppants
Segment Reporting Information
Total sales									414,897	1,010,521
Oil & Gas Proppants | Operating Segments
Segment Reporting Information
Total sales									414,897	1,010,521	1,182,991
Total segment contribution margin									142,041	248,594	357,846
Industrial & Specialty Products
Segment Reporting Information
Total sales									430,988	463,956
Industrial & Specialty Products | Operating Segments
Segment Reporting Information
Total sales									430,988	463,956	394,307
Total segment contribution margin									$ 159,176	$ 178,215	$ 155,084

Unaudited Supplementary Data (D

Unaudited Supplementary Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Sales:
Total sales									$ 845,885	$ 1,474,477	$ 1,577,298
Cost of sales (excluding depreciation, depletion and amortization):
Total cost of sales (excluding depreciation, depletion and amortization)									575,070	1,133,293	1,163,129
Operating expenses:
Selling, general and administrative	$ 27,777	$ 27,216	$ 39,126	$ 30,052	$ 37,325	$ 40,208	$ 38,659	$ 34,656	124,171	150,848	146,971
Depreciation, depletion and amortization	39,964	40,069	37,086	38,449	42,819	47,126	44,899	44,600	155,568	179,444	148,832
Goodwill and other asset impairments	2,644	222	3,956	103,866	363,717	130	0	0	110,688	363,847	281,899
Total operating expenses	70,385	67,507	80,168	172,367	443,861	87,464	83,558	79,256	390,427	694,139	577,702
Operating loss	15,474	1,373	(32,374)	(104,085)	(362,764)	(9,283)	17,136	1,956	(119,612)	(352,955)	(163,533)
Other (expense) income:
Interest expense	(16,155)	(19,274)	(22,179)	(22,277)	(22,996)	(24,733)	(23,765)	(23,978)	(79,885)	(95,472)	(70,564)
Other income (expense), net, including interest income	8,758	(409)	(1,670)	17,671	443	3,280	15,074	722	24,350	19,519	4,144
Total other expense	(7,397)	(19,683)	(23,849)	(4,606)	(22,553)	(21,453)	(8,691)	(23,256)	(55,535)	(75,953)	(66,420)
Loss before income taxes	8,077	(18,310)	(56,223)	(108,691)	(385,317)	(30,736)	8,445	(21,300)	(175,147)	(428,908)	(229,953)
Income tax benefit	(3,760)	4,094	23,605	36,086	91,892	7,671	(2,384)	1,972	60,025	99,151	29,132
Net loss	4,317	(14,216)	(32,618)	(72,605)	(293,425)	(23,065)	6,061	(19,328)	(115,122)	(329,757)	(200,821)
Less: Net loss attributable to non-controlling interest	(250)	(254)	(264)	(260)	(554)	(28)	(89)	(4)	(1,028)	(675)	(13)
Net loss attributable to U.S. Silica Holdings, Inc.	$ 4,567	$ (13,962)	$ (32,354)	$ (72,345)	$ (292,871)	$ (23,037)	$ 6,150	$ (19,324)	$ (114,094)	$ (329,082)	$ (200,808)
Basic loss per share (in dollars per share)	$ 0.06	$ (0.19)	$ (0.44)	$ (0.98)	$ (4)	$ (0.31)	$ 0.08	$ (0.26)	$ (1.55)	$ (4.49)	$ (2.63)
Diluted loss per share (in dollars per share)	$ 0.06	$ (0.19)	$ (0.44)	$ (0.98)	$ (4)	$ (0.31)	$ 0.08	$ (0.26)	$ (1.55)	$ (4.49)	$ (2.63)
Weighted average shares outstanding (shares)	73,728	73,688	73,620	73,467	73,343	73,328	73,301	73,040	73,634	73,253	76,453
Weighted average common shares outstanding, diluted (in shares)	74,328	73,688	73,620	73,467	73,343	73,328	73,505	73,040
Dividends declared per share (in dollars per share)	$ 0	$ 0	$ 0	$ 0.02	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.02	$ 0.25	$ 0.25
Product
Sales:
Total sales	$ 190,189	$ 159,637	$ 160,200	$ 222,161	$ 280,594	$ 287,977	$ 303,041	$ 296,860	$ 732,187	$ 1,168,472	$ 1,282,799
Cost of sales (excluding depreciation, depletion and amortization):
Total cost of sales (excluding depreciation, depletion and amortization)	113,609	93,747	114,130	165,496	212,905	226,797	225,473	234,916	486,982	900,091	955,469
Service
Sales:
Total sales	37,088	16,835	12,337	47,438	58,465	73,837	91,813	81,890	113,698	306,005	294,499
Cost of sales (excluding depreciation, depletion and amortization):
Total cost of sales (excluding depreciation, depletion and amortization)	$ 27,809	$ 13,845	$ 10,613	$ 35,821	$ 45,057	$ 56,836	$ 68,687	$ 62,622	$ 88,088	$ 233,202	$ 207,660

Parent Company Financials - Con

Parent Company Financials - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 150,920	$ 185,740
Total current assets	486,313	509,040
Total assets	2,246,947	2,553,234
Current Liabilities:
Accounts payable and accrued expenses	121,920	248,237
Total current liabilities	194,895	335,398
Total liabilities	1,620,156	1,836,654
Stockholders’ Equity:
Preferred stock	0	0
Common stock	827	823
Additional paid-in capital	1,200,023	1,185,116
Retained deficit	(395,496)	(279,956)
Treasury stock, at cost	(181,615)	(180,912)
Accumulated other comprehensive loss	(8,479)	(19,854)
Total U.S. Silica Holdings, Inc. stockholders’ equity	615,260	705,217
Non-controlling interest	11,531	11,363
Total stockholders' equity	626,791	716,580	$ 1,052,304	$ 1,396,506
Total liabilities and stockholders’ equity	2,246,947	2,553,234
Parent Company
Current Assets:
Cash and cash equivalents	46,851	51,849
Due from affiliates	168,276	138,988
Total current assets	215,127	190,837
Investment in subsidiaries	412,169	530,830
Total assets	627,296	721,667
Current Liabilities:
Accounts payable and accrued expenses	286	129
Dividends payable	219	4,958
Total current liabilities	505	5,087
Total liabilities	505	5,087
Stockholders’ Equity:
Preferred stock	0	0
Common stock	827	823
Additional paid-in capital	1,200,023	1,185,116
Retained deficit	(395,496)	(279,956)
Treasury stock, at cost	(181,615)	(180,912)
Accumulated other comprehensive loss	(8,479)	(19,854)
Total U.S. Silica Holdings, Inc. stockholders’ equity	615,260	705,217
Non-controlling interest	11,531	11,363
Total stockholders' equity	626,791	716,580	$ 1,052,304	$ 1,396,506
Total liabilities and stockholders’ equity	$ 627,296	$ 721,667

Parent Company Financials - C_2

Parent Company Financials - Condensed Statements of Operations and Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Income Statements, Captions [Line Items]
Total sales									$ 845,885	$ 1,474,477	$ 1,577,298
Cost of sales									575,070	1,133,293	1,163,129
Operating expenses:
Selling, general and administrative	$ 27,777	$ 27,216	$ 39,126	$ 30,052	$ 37,325	$ 40,208	$ 38,659	$ 34,656	124,171	150,848	146,971
Total operating expenses	70,385	67,507	80,168	172,367	443,861	87,464	83,558	79,256	390,427	694,139	577,702
Operating loss	15,474	1,373	(32,374)	(104,085)	(362,764)	(9,283)	17,136	1,956	(119,612)	(352,955)	(163,533)
Other income (expense)
Total other expense	(7,397)	(19,683)	(23,849)	(4,606)	(22,553)	(21,453)	(8,691)	(23,256)	(55,535)	(75,953)	(66,420)
Income tax benefit	(3,760)	4,094	23,605	36,086	91,892	7,671	(2,384)	1,972	60,025	99,151	29,132
Net loss	4,317	(14,216)	(32,618)	(72,605)	(293,425)	(23,065)	6,061	(19,328)	(115,122)	(329,757)	(200,821)
Less: Net loss attributable to non-controlling interest	(250)	(254)	(264)	(260)	(554)	(28)	(89)	(4)	(1,028)	(675)	(13)
Net loss attributable to U.S. Silica Holdings, Inc.	$ 4,567	$ (13,962)	$ (32,354)	$ (72,345)	$ (292,871)	$ (23,037)	$ 6,150	$ (19,324)	(114,094)	(329,082)	(200,808)
Other comprehensive (loss) income
Unrealized gain (loss) on derivatives (net of tax of $973, $(456), and $(470) for 2020, 2019, and 2018, respectively)									3,053	(1,432)	(1,545)
Foreign currency translation adjustment (net of tax of $444, $(60), and $(196) for 2020, 2019 and 2018, respectively)									1,391	(188)	(614)
Pension and other post-retirement benefits liability adjustments (net of tax of $2,207, $(1,024), and $339 for 2020, 2019 and 2018, respectively)									6,931	(3,214)	1,065
Comprehensive loss									(103,747)	(334,591)	(201,915)
Less: Comprehensive loss attributable to non-controlling interest									(1,028)	(675)	(13)
Comprehensive loss attributable to U.S. Silica Holdings, Inc.									(102,719)	(333,916)	(201,902)
Tax expense (benefit) on unrealized gain (loss) on derivatives									973	(456)	(470)
Tax expense (benefit) on foreign currency translation adjustment									444	(60)	(196)
Tax (expense) benefit on pension and other post-retirement benefits liability adjustment									2,207	(1,024)	339
Parent Company
Condensed Income Statements, Captions [Line Items]
Total sales									0	0	0
Cost of sales									0	0	0
Operating expenses:
Selling, general and administrative									253	253	254
Total operating expenses									253	253	254
Operating loss									(253)	(253)	(254)
Other income (expense)
Interest income									210	1,440	2,784
Total other expense									210	1,440	2,784
(Loss) income before income taxes and equity in net earnings of subsidiaries									(43)	1,187	2,530
Income tax benefit									0	(327)	(696)
(Loss) income before equity in net earnings of subsidiaries									(43)	860	1,834
Equity in earnings of subsidiaries, net of tax									(115,079)	(330,617)	(202,655)
Net loss									(115,122)	(329,757)	(200,821)
Less: Net loss attributable to non-controlling interest									(1,028)	(675)	(13)
Net loss attributable to U.S. Silica Holdings, Inc.									(114,094)	(329,082)	(200,808)
Other comprehensive (loss) income
Unrealized gain (loss) on derivatives (net of tax of $973, $(456), and $(470) for 2020, 2019, and 2018, respectively)									3,053	(1,432)	(1,545)
Foreign currency translation adjustment (net of tax of $444, $(60), and $(196) for 2020, 2019 and 2018, respectively)									1,391	(188)	(614)
Pension and other post-retirement benefits liability adjustments (net of tax of $2,207, $(1,024), and $339 for 2020, 2019 and 2018, respectively)									6,931	(3,214)	1,065
Comprehensive loss									(103,747)	(334,591)	(201,915)
Less: Comprehensive loss attributable to non-controlling interest									(1,028)	(675)	(13)
Comprehensive loss attributable to U.S. Silica Holdings, Inc.									(102,719)	(333,916)	(201,902)
Tax expense (benefit) on unrealized gain (loss) on derivatives									973	(456)	(470)
Tax expense (benefit) on foreign currency translation adjustment									444	(60)	(196)
Tax (expense) benefit on pension and other post-retirement benefits liability adjustment									$ 2,207	$ (1,024)	$ 339

Parent Company Financials - C_3

Parent Company Financials - Condensed Statements of Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				$ 716,580				$ 1,052,304	$ 716,580	$ 1,052,304	$ 1,396,506
Net loss	$ 4,317	$ (14,216)	$ (32,618)	$ (72,605)	$ (293,425)	$ (23,065)	$ 6,061	$ (19,328)	(115,122)	(329,757)	(200,821)
Unrealized gain (loss) on derivatives									3,053	(1,432)	(1,545)
Foreign currency translation adjustment									1,391	(188)	(614)
Pension and post-retirement liability									6,931	(3,214)	1,065
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)									(1,446)	(18,728)	(19,330)
Contributions from non-controlling interest									1,196	4,554	7,497
Equity-based compensation									14,911	15,906	22,337
Proceeds from options exercised										128	61
Shares withheld for tax payments related to vested restricted stock and stock units									(703)	(2,993)	(4,383)
Repurchase of common stock											(148,469)
Ending Balance	$ 626,791				$ 716,580				$ 626,791	$ 716,580	$ 1,052,304
Dividends declared per share (in dollars per share)	$ 0	$ 0	$ 0	$ 0.02	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.02	$ 0.25	$ 0.25
Total U.S. Silica Holdings Inc., Stockholders’ Equity
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				$ 705,217				$ 1,044,820	$ 705,217	$ 1,044,820	$ 1,396,506
Net loss									(114,094)	(329,082)	(200,808)
Unrealized gain (loss) on derivatives									3,053	(1,432)	(1,545)
Foreign currency translation adjustment									1,391	(188)	(614)
Pension and post-retirement liability									6,931	(3,214)	1,065
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)									(1,446)	(18,728)	(19,330)
Equity-based compensation									14,911	15,906	22,337
Proceeds from options exercised										128	61
Shares withheld for tax payments related to vested restricted stock and stock units									(703)	(2,993)	(4,383)
Repurchase of common stock											(148,469)
Ending Balance	$ 615,260				$ 705,217				615,260	705,217	1,044,820
Common Stock
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				823				818	823	818	812
Shares withheld for tax payments related to vested restricted stock and stock units									4	5	6
Ending Balance	827				823				827	823	818
Treasury Stock
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				(180,912)				(178,215)	(180,912)	(178,215)	(25,456)
Proceeds from options exercised										296	93
Shares withheld for tax payments related to vested restricted stock and stock units									(703)	(2,993)	(4,383)
Repurchase of common stock											(148,469)
Ending Balance	(181,615)				(180,912)				(181,615)	(180,912)	(178,215)
Additional Paid-In Capital
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				1,185,116				1,169,383	1,185,116	1,169,383	1,147,084
Equity-based compensation									14,911	15,906	22,337
Proceeds from options exercised										(168)	(32)
Shares withheld for tax payments related to vested restricted stock and stock units									(4)	(5)	(6)
Ending Balance	1,200,023				1,185,116				1,200,023	1,185,116	1,169,383
Retained Earnings (Deficit)
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				(279,956)				67,854	(279,956)	67,854	287,992
Net loss									(114,094)	(329,082)	(200,808)
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)									(1,446)	(18,728)	(19,330)
Ending Balance	(395,496)				(279,956)				(395,496)	(279,956)	67,854
Accumulated Other Comprehensive Loss
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				(19,854)				(15,020)	(19,854)	(15,020)	(13,926)
Unrealized gain (loss) on derivatives									3,053	(1,432)	(1,545)
Foreign currency translation adjustment									1,391	(188)	(614)
Pension and post-retirement liability									6,931	(3,214)	1,065
Ending Balance	(8,479)				(19,854)				(8,479)	(19,854)	(15,020)
Non-controlling Interest
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				11,363				7,484	11,363	7,484	0
Net loss									(1,028)	(675)	(13)
Contributions from non-controlling interest									1,196	4,554	7,497
Ending Balance	11,531				11,363				11,531	11,363	7,484
Parent Company
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				716,580				1,052,304	716,580	1,052,304	1,396,506
Net loss									(115,122)	(329,757)	(200,821)
Unrealized gain (loss) on derivatives									3,053	(1,432)	(1,545)
Foreign currency translation adjustment									1,391	(188)	(614)
Pension and post-retirement liability									6,931	(3,214)	1,065
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)									(1,446)	(18,728)	(19,330)
Contributions from non-controlling interest									1,196	4,554
Equity-based compensation									14,911	15,906	22,337
Proceeds from options exercised										128	61
Shares withheld for tax payments related to vested restricted stock and stock units									(703)	(2,993)	(4,383)
Repurchase of common stock											(148,469)
Ending Balance	626,791				716,580				$ 626,791	$ 716,580	$ 1,052,304
Dividends declared per share (in dollars per share)									$ 0.02	$ 0.25	$ 0.25
Parent Company | Total U.S. Silica Holdings Inc., Stockholders’ Equity
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				705,217				1,044,820	$ 705,217	$ 1,044,820	$ 1,396,506
Net loss									(114,094)	(329,082)	(200,808)
Unrealized gain (loss) on derivatives									3,053	(1,432)	(1,545)
Foreign currency translation adjustment									1,391	(188)	(614)
Pension and post-retirement liability									6,931	(3,214)	1,065
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)									(1,446)	(18,728)	(19,330)
Equity-based compensation									14,911	15,906	22,337
Proceeds from options exercised										128	61
Shares withheld for tax payments related to vested restricted stock and stock units									(703)	(2,993)	(4,383)
Repurchase of common stock											(148,469)
Ending Balance	615,260				705,217				615,260	705,217	1,044,820
Parent Company | Common Stock
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				823				818	823	818	812
Shares withheld for tax payments related to vested restricted stock and stock units									4	5	6
Ending Balance	827				823				827	823	818
Parent Company | Treasury Stock
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				(180,912)				(178,215)	(180,912)	(178,215)	(25,456)
Proceeds from options exercised										296	93
Shares withheld for tax payments related to vested restricted stock and stock units									(703)	(2,993)	(4,383)
Repurchase of common stock											(148,469)
Ending Balance	(181,615)				(180,912)				(181,615)	(180,912)	(178,215)
Parent Company | Additional Paid-In Capital
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				1,185,116				1,169,383	1,185,116	1,169,383	1,147,084
Equity-based compensation									14,911	15,906	22,337
Proceeds from options exercised										(168)	(32)
Shares withheld for tax payments related to vested restricted stock and stock units									(4)	(5)	(6)
Ending Balance	1,200,023				1,185,116				1,200,023	1,185,116	1,169,383
Parent Company | Retained Earnings (Deficit)
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				(279,956)				67,854	(279,956)	67,854	287,992
Net loss									(114,094)	(329,082)	(200,808)
Cash dividend declared ($0.25 per share for 2020, 2019 and 2018, respectively)									(1,446)	(18,728)	(19,330)
Ending Balance	(395,496)				(279,956)				(395,496)	(279,956)	67,854
Parent Company | Accumulated Other Comprehensive Loss
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				(19,854)				(15,020)	(19,854)	(15,020)	(13,926)
Unrealized gain (loss) on derivatives									3,053	(1,432)	(1,545)
Foreign currency translation adjustment									1,391	(188)	(614)
Pension and post-retirement liability									6,931	(3,214)	1,065
Ending Balance	(8,479)				(19,854)				(8,479)	(19,854)	(15,020)
Parent Company | Non-controlling Interest
Condensed Stockholders' Equity Statement [Line Items]
Beginning Balance				$ 11,363				$ 7,484	11,363	7,484	0
Net loss									(1,028)	(675)	(13)
Contributions from non-controlling interest									1,196	4,554
Ending Balance	$ 11,531				$ 11,363				$ 11,531	$ 11,363	$ 7,484

Parent Company Financials - C_4

Parent Company Financials - Condensed Statements of Cash Flows (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Net loss	$ 4,317,000	$ (14,216,000)	$ (32,618,000)	$ (72,605,000)	$ (293,425,000)	$ (23,065,000)	$ 6,061,000	$ (19,328,000)	$ (115,122,000)	$ (329,757,000)	$ (200,821,000)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Accounts payable and accrued expenses									(86,734,000)	21,024,000	26,907,000
Net cash (used in) provided by operating activities									(10,534,000)	144,046,000	310,706,000
Investing activities:
Net cash used in investing activities									(27,564,000)	(120,393,000)	(1,066,879,000)
Financing activities:
Dividends paid									(6,185,000)	(18,592,000)	(19,912,000)
Repurchase of common stock									0	0	(148,469,000)
Proceeds from options exercised									0	128,000	61,000
Tax payments related to shares withheld for vested restricted stock and stock units									(703,000)	(2,993,000)	(4,383,000)
Contributions from non-controlling interest									1,196,000	4,554,000	7,497,000
Net cash provided by (used in) financing activities									3,278,000	(40,411,000)	574,104,000
Cash and cash equivalents, beginning of period				185,740,000				202,498,000	185,740,000	202,498,000	384,567,000
Cash and cash equivalents, end of period	150,920,000				185,740,000				150,920,000	185,740,000	202,498,000
Cash (received) paid during the period for:
Interest									(73,695,000)	(87,286,000)	(66,769,000)
Cash dividends paid to the parent by its consolidated entities									0	0	0
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net loss									(115,122,000)	(329,757,000)	(200,821,000)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Undistributed loss (income) from equity method investment, net									115,079,000	330,617,000	202,655,000
Accounts payable and accrued expenses									155,000	(88,000)	(295,000)
Net cash (used in) provided by operating activities									112,000	772,000	1,539,000
Investing activities:
Investment in subsidiary									0	0	0
Net cash used in investing activities									0	0	0
Financing activities:
Dividends paid									(6,185,000)	(18,592,000)	(19,912,000)
Repurchase of common stock									0	0	(148,469,000)
Proceeds from options exercised									0	128,000	61,000
Tax payments related to shares withheld for vested restricted stock and stock units									(703,000)	(2,993,000)	(4,383,000)
Contributions from non-controlling interest									1,196,000	4,554,000	7,497,000
Net financing activities with subsidiaries									582,000	(39,171,000)	40,171,000
Net cash provided by (used in) financing activities									(5,110,000)	(56,074,000)	(125,035,000)
Net decrease in cash and cash equivalents									(4,998,000)	(55,302,000)	(123,496,000)
Cash and cash equivalents, beginning of period				$ 51,849,000				$ 107,151,000	51,849,000	107,151,000	230,647,000
Cash and cash equivalents, end of period	$ 46,851,000				$ 51,849,000				46,851,000	51,849,000	107,151,000
Cash (received) paid during the period for:
Interest									$ (210,000)	$ (1,440,000)	$ (2,784,000)

Impairments (Details)

Impairments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Text Block Supplement [Abstract]
Inventories, net									$ 6,837	$ 4,100	$ 3,316
Property, plant and mine development, net									11,822	243,064	109,938
Operating lease right-of-use assets									3,406	115,443	0
Goodwill									86,100	0	164,167
Intangible assets, net									2,523	1,240	4,478
Total	$ 2,644	$ 222	$ 3,956	$ 103,866	$ 363,717	$ 130	$ 0	$ 0	$ 110,688	$ 363,847	$ 281,899

Impairments - Narrative (Detail

Impairments - Narrative (Details) - Industrial & Specialty Products - Goodwill And Other Assets Impairments $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Technology and intellectual property
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of finite-lived intangibles	$ 1,400
Trade names
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of indefinite-lived intangibles	$ 1,100