CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Operating activities
Net loss			$ (53,821)	$ (235,731)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	$ 8,683	$ 11,532	26,652	34,923
Amortization of debt issuance costs and original issue discount			513	882
Provision for doubtful accounts			145	493
Deferred income taxes			(167)	76
(Gain) loss on disposal or impairment of assets			(1,097)	125,738
Loss on sale of Russian proppant business			350	25,101
Foreign currency transaction gain, net			0	(35)
Stock compensation expense			3,027	3,831
PIK accrual on notes payable, related parties			0	997
Change in fair value of derivative instruments			(1,974)	(575)
Changes in operating assets and liabilities:
Trade accounts and other receivables			(109)	(14,538)
Inventories			5,132	5,567
Prepaid expenses and other current assets			104	(245)
Accounts payable			(4,044)	8,795
Accrued expenses			(2,413)	3,561
Income tax receivable, net			92	(1,069)
Other, net			2,757	2,123
Net cash used in operating activities			(24,853)	(40,106)
Investing activities
Capital expenditures			(1,668)	(2,095)
Net proceeds from asset sales			5,233	21,501
Net cash provided by investing activities			3,565	19,406
Financing activities
Proceeds from long-term debt			0	12,349
Repayments on long-term debt			0	(3,250)
Repayments on insurance financing agreement			(941)	(923)
Payments of debt issuance costs			0	(989)
Purchase of common stock			(421)	(534)
Net cash provided by financing activities			1,487	6,653
Effect of exchange rate changes on cash			0	246
Net decrease in cash and cash equivalents and restricted cash			(19,801)	(13,801)
Cash and cash equivalents and restricted cash at beginning of period			78,385	91,680	$ 91,680
Cash and cash equivalents and restricted cash at end of period	$ 58,584	$ 77,879	58,584	77,879	$ 78,385
Supplemental cash flow information
Interest paid			6,751	2,319
Income taxes paid			0	465
ATM Program
Financing activities
Proceeds from sale of common stock under ATM program			$ 2,849	$ 0