Condended Financial Information of Registrant Statements of Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income (loss)	$ 13,886	$ (5,822)	$ 16,178	$ 15,185	$ 19,005	$ 18,824	$ 7,006	$ 27,786	$ 39,427	$ 72,621	$ (45,835)
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation, depletion, and amortization									52,642	45,989	31,617
Non-cash interest expense									7,127	7,276	18,121
Change in value of common stock warrants									(1,801)	1,674	(2,962)
Deferred taxes									661	(1,321)	(7,935)
Stock-based compensation									6,196	7,204	6,625
Equity in losses (income) of subsidiaries									(9,464)	(18,369)	22,381
Net changes in operating assets and liabilities:
Prepaid and other assets									(5,521)	37,645	945
Accounts payable and other accrued liabilities									19,885	(33,780)	(26,698)
Net cash provided by (used in) operating activities									90,620	106,483	(23,393)
Cash flows from investing activities:
Capital expenditures									(48,439)	(31,708)	(24,833)
Net cash used in investing activities									(175,821)	(31,673)	(286,243)
Cash flows from financing activities:
Proceeds from sale of common stock, net of offering costs									19,318	0	49,044
Proceeds from borrowings									118,741	616,706	354,682
Repayments of borrowings									(118,751)	(603,770)	(202,165)
Payment of deferred loan costs									(379)	(10,064)	(6,892)
Other financing activities, net									(860)	(993)	(598)
Net cash provided by (used in) financing activities									41,943	(4,751)	190,118
Net increase (decrease) in cash, cash equivalents, and restricted cash									(43,258)	70,059	(119,518)
Cash, cash equivalents, and restricted cash at beginning of period				119,077				49,018	119,077	49,018	168,536
Cash, cash equivalents, and restricted cash at end of period	75,819				119,077				75,819	119,077	49,018
Net cash received (paid) for:
Interest									(28,186)	(23,873)	(13,217)
Taxes									49	(1,478)	589
Non-cash investing and financing activities:
Accrued capital expenditures									6,199	2,926	4,907
Value of warrants and debt reclassified to equity									0	0	3,084
Capital lease additions									1,678	165	1,575
Parent Company
Cash flows from operating activities:
Net income (loss)									39,427	72,621	(45,835)
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation, depletion, and amortization									4,092	2,871	2,205
Non-cash interest expense									4,925	5,617	13,722
Non-cash interest income from subsidiary									0	0	(583)
Change in value of common stock warrants									(1,801)	1,674	(2,962)
Deferred taxes									0	0	(8,573)
Stock-based compensation									6,196	7,204	2,226
Equity in losses (income) of subsidiaries									(81,942)	(111,162)	17,170
Debt extinguishment and commitment costs									0	1,804	0
Net changes in operating assets and liabilities:
Prepaid and other assets									(2,604)	(2,568)	23
Accounts payable and other accrued liabilities									5,601	3,088	381
Net cash provided by (used in) operating activities									(26,106)	(18,851)	(22,226)
Cash flows from investing activities:
Investments in subsidiaries									0	(2,072)	(264,163)
Distributions from subsidiaries									0	70,645	9,047
Note receivable from subsidiary									0	0	10,000
Capital expenditures									(3,682)	(5,366)	(4,321)
Due to (from) subsidiaries									(25,102)	80,762	(23,947)
Net cash used in investing activities									(28,784)	143,969	(273,384)
Cash flows from financing activities:
Proceeds from sale of common stock, net of offering costs									19,318	0	49,044
Proceeds from borrowings									10,770	0	172,282
Repayments of borrowings									(11,253)	(68,873)	(63,062)
Payment of deferred loan costs									0	0	(6,298)
Due to (from) subsidiaries									0	0	63,578
Other financing activities, net									(860)	(993)	(598)
Net cash provided by (used in) financing activities									17,975	(69,866)	214,946
Net increase (decrease) in cash, cash equivalents, and restricted cash									(36,915)	55,252	(80,664)
Cash, cash equivalents, and restricted cash at beginning of period				$ 66,359				$ 11,107	66,359	11,107	91,771
Cash, cash equivalents, and restricted cash at end of period	$ 29,444				$ 66,359				29,444	66,359	11,107
Net cash received (paid) for:
Interest									(5,750)	(7,856)	(4,557)
Taxes									(49)	(1,478)	0
Non-cash investing and financing activities:
Accrued capital expenditures									714	370	361
Value of warrants and debt reclassified to equity									0	0	3,084
Capital lease additions									$ 539	$ 165	$ 1,575