CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Operating activities
Net loss			$ (37,084)	$ (57,266)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	$ 8,944	$ 11,509	17,969	23,391
Amortization of debt issuance costs and original issue discount			340	710
Provision for doubtful accounts			81	413
Deferred income taxes			4	618
Gain on disposal or impairment of assets	(55)	0	(59)	0
Loss on sale of Russian proppant business	350	0	350	0
Foreign currency transaction loss, net			0	2
Stock compensation expense			2,254	2,750
PIK accrual on notes payable, related parties			0	997
Change in fair value of derivative instruments			(1,348)	159
Changes in operating assets and liabilities:
Trade accounts and other receivables			(3,777)	(14,128)
Inventories			836	4,689
Prepaid expenses and other current assets			(407)	(553)
Accounts payable			(1,341)	1,214
Accrued expenses			(4,303)	1,853
Income tax receivable, net			97	(1,171)
Other, net			2,126	1,405
Net cash used in operating activities			(24,262)	(34,917)
Investing activities
Capital expenditures			(1,105)	(1,176)
Net cash used in investing activities			(1,105)	(1,176)
Financing activities
Repayments on long-term debt			0	(3,250)
Repayments on insurance financing agreement			(500)	(551)
Payments of debt issuance costs			0	(875)
Purchase of common stock			(421)	(533)
Net cash provided by (used in) financing activities			1,928	(5,209)
Effect of exchange rate changes on cash			0	249
Net decrease in cash and cash equivalents and restricted cash			(23,439)	(41,053)
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	$ 54,946	$ 50,627	54,946	50,627	$ 78,385
Supplemental cash flow information
Interest paid			3,850	761
Income taxes paid			0	0
ATM Program
Financing activities
Proceeds from sale of common stock under ATM program			$ 2,849	$ 0