Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net (loss) income	$ 138,007	$ (97,057)	$ (679,524)
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Unrealized (gain) loss on derivatives	(9,715)	41,238	39,265
Depletion, depreciation and amortization	177,502	122,048	178,847
Accretion of asset retirement obligations	1,290	1,182	734
Full-cost ceiling impairment	0	158,633	801,166
Stock-based compensation expense	16,654	12,362	9,450
Deferred income tax benefit	0	0	(150,327)
Amortization of debt issuance cost	468	1,148	852
Net gain on asset sales and inventory impairment	(23)	(107,277)	(908)
Changes in operating assets and liabilities
Accounts receivable	(82,549)	(14,259)	3,633
Lease and well equipment inventory	(3,623)	(700)	(180)
Prepaid expenses	(2,960)	(124)	(544)
Other assets	(6,425)	490	(552)
Accounts payable, accrued liabilities and other current liabilities	33,559	6,611	1,375
Royalties payable	37,370	7,495	1,654
Advances from joint interest owners	1,089	1,000	700
Income taxes payable	0	(2,848)	2,405
Other long-term liabilities	(1,519)	4,144	489
Net cash provided by operating activities	299,125	134,086	208,535
Investing activities
Oil and natural gas properties capital expenditures	(699,445)	(379,067)	(432,715)
Expenditures for other property and equipment	(120,816)	(74,845)	(64,499)
Proceeds from sale of assets	977	5,173	139,836
Business combination, net of cash acquired	0	0	(24,028)
Restricted cash	0	43,098	(43,098)
Restricted cash in less-than-wholly-owned subsidiaries	(4,719)	1	(650)
Net cash used in investing activities	(824,003)	(405,640)	(425,154)
Financing activities
Repayments of borrowings	0	(120,000)	(476,982)
Borrowings under Credit Agreement	0	120,000	125,000
Proceeds from issuance of common stock	208,720	288,510	188,720
Proceeds from issuance of senior unsecured notes	0	184,625	400,000
Cost to issue equity	(280)	(847)	(1,158)
Cost to issue senior unsecured notes	0	(2,734)	(9,598)
Proceeds from stock options exercised	2,920	100	10
Capital commitments from non-controlling interest owners of less-than-wholly-owned subsidiaries	0	0	562
Contributions related to formation of Joint Venture	171,500	0	0
Capital contribution from non-controlling interest owners in less-than-wholly-owned subsidiaries	44,100	0	0
Distributions to non-controlling interest owners of less-than-wholly-owned subsidiaries	10,045	0	0
Taxes paid related to net share settlement of stock-based compensation	5,763	1,948	1,610
Purchase of non-controlling interest of less-than-wholly-owned subsidiary	(2,653)	0	0
Net cash provided by financing activities	408,499	467,706	224,944
(Decrease) increase in cash	(116,379)	196,152	8,325
Cash at beginning of year	212,884	16,732	8,407
Cash at end of year	$ 96,505	$ 212,884	$ 16,732