CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (in thousands, except share data) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018		Jun. 30, 2018		Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 615,906		$ 615,906		$ 313,943
Accounts receivable	178,682		178,682		160,154
Derivative assets	146,329		146,329		64,266
Prepaid expenses and other	14,293		14,293		10,752
Total current assets	955,210		955,210		549,115
Property and equipment (successful efforts method):
Proved oil and gas properties	6,372,956		6,372,956		6,139,379
Accumulated depletion, depreciation, and amortization	(3,041,653)		(3,041,653)		(3,171,575)
Unproved oil and gas properties	1,917,883		1,917,883		2,047,203
Wells in progress	361,238		361,238		321,347
Oil and gas properties held for sale, net	5,040		5,040		111,700
Other property and equipment, net of accumulated depreciation of $53,483 and $49,985, respectively	102,986		102,986		106,738
Total property and equipment, net	5,718,450		5,718,450		5,554,792
Noncurrent assets:
Derivative assets	31,151		31,151		40,362
Other noncurrent assets	31,674		31,674		32,507
Total noncurrent assets	62,825		62,825		72,869
Total assets	6,736,485		6,736,485		6,176,776
Current liabilities:
Accounts payable and accrued expenses	446,318		446,318		386,630
Current portion of Senior Notes, net of unamortized deferred financing costs (note 5)	342,301		342,301		0
Derivative liabilities	259,338		259,338		172,582
Total current liabilities	1,047,957		1,047,957		559,212
Noncurrent liabilities:
Revolving credit facility	0		0		0
Noncurrent portion of Senior Notes, net of unamortized deferred financing costs	2,429,994		2,429,994		2,769,663
Senior Convertible Notes, net of unamortized discount and deferred financing costs	143,430		143,430		139,107
Asset retirement obligations	87,279		87,279		103,026
Asset retirement obligations associated with oil and gas properties held for sale	0		0		11,369
Deferred income taxes	177,709		177,709		79,989
Derivative liabilities	67,583		67,583		71,402
Other noncurrent liabilities	45,906		45,906		48,400
Total noncurrent liabilities	2,951,901		2,951,901		3,222,956
Commitments and contingencies (note 6)
Stockholders’ equity:
Common stock, $0.01 par value - authorized: 200,000,000 shares; issued and outstanding: 111,846,998 and 111,687,016 shares, respectively	1,118		1,118		1,117
Additional paid-in capital	1,754,169		1,754,169		1,741,623
Retained earnings	997,641	[1]	997,641	[1]	665,657
Accumulated other comprehensive loss	(16,301)	[1]	(16,301)	[1]	(13,789)
Total stockholders’ equity	2,736,627		2,736,627		2,394,608
Total liabilities and stockholders’ equity	6,736,485		6,736,485		6,176,776
Exploration	14,056		27,783
6.50% Senior Notes due 2021 | Senior Notes [Member]
Current liabilities:
Current portion of Senior Notes, net of unamortized deferred financing costs (note 5)	$ 342,301		$ 342,301
Noncurrent liabilities:
Noncurrent portion of Senior Notes, net of unamortized deferred financing costs					$ 341,955

[1] (1) The Company reclassified $3.0 million of tax effects stranded in accumulated other comprehensive loss to retained earnings as of January 1, 2018. Please refer to Note 1 - Summary of Significant Accounting Policies for further detail.