Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Results of Operations, Revenue from Oil and Gas Producing Activities									$ 1,307,275	$ 1,389,961	$ 913,084
Commodity price risk management gain (loss), net									(162,844)	145,237	(3,936)
Other income									11,692	13,461	12,468
Total revenues	$ 265,022	$ 365,943	$ 390,658	$ 134,500	$ 794,811	$ 280,717	$ 212,531	$ 260,600	1,156,123	1,548,659	921,616
Costs, expenses and other:
Lease operating expenses									142,248	130,957	89,641
Production taxes									80,754	90,357	60,717
Transportation, gathering and processing expenses									46,353	37,403	33,220
Exploration, geologic and geophysical expense									4,054	6,204	47,334
Impairment of properties and equipment									38,536	458,397	285,887
Impairment of goodwill									0	0	75,121
General and administrative expense									161,753	170,504	120,370
Depreciation, depletion and amortization									644,152	559,793	469,084
Accretion of asset retirement obligations									6,117	5,075	6,306
(Gain) loss on sale of properties and equipment									9,734	394	(766)
Provision for uncollectible notes receivable									0	0	40,203
Other expenses									11,317	11,829	13,157
Total costs, expenses and other	267,713	321,562	280,623	275,120	538,626	270,593	400,770	260,924	1,145,018	1,470,913	1,159,868
Income (loss) from operations	(2,691)	44,381	110,035	(140,620)	256,185	10,124	(188,239)	(324)	11,105	77,746	(238,252)
Loss on extinguishment of debt									0	0	24,747
Interest expense									(71,171)	(70,730)	(78,694)
Interest income									72	413	2,261
Income (loss) before income taxes	(20,111)	26,570	91,135	(157,588)	238,024	(7,310)	(205,580)	(17,705)	(59,994)	7,429	(339,432)
Income tax (expense) benefit									3,322	(5,406)	211,928
Net income (loss)	$ (20,952)	$ 15,908	$ 68,548	$ (120,176)	$ 178,853	$ (3,434)	$ (160,257)	$ (13,139)	$ (56,672)	$ 2,023	$ (127,504)
Earnings per share attributable to shareholders:
Basic	$ (0.34)	$ 0.25	$ 1.04	$ (1.82)	$ 2.71	$ (0.05)	$ (2.43)	$ (0.20)	$ (0.89)	$ 0.03	$ (1.94)
Diluted	$ (0.34)	$ 0.25	$ 1.04	$ (1.82)	$ 2.71	$ (0.05)	$ (2.43)	$ (0.20)	$ (0.89)	$ 0.03	$ (1.94)
Weighted-average common shares outstanding:
Basic									64,032	66,059	65,837
Diluted									64,032	66,303	65,837