Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (127,504)	$ (245,928)	$ (68,280)
Adjustments to net income (loss) to reconcile to net cash provided by operating activities:
Net change in fair value of unsettled commodity derivatives	17,260	333,770	35,791
Depreciation, depletion and amortization	469,084	416,874	303,258
Provision for uncollectible notes receivable	(40,203)	44,038	0
Impairment of properties and equipment	285,887	9,973	161,620
Impairment of goodwill	75,121	0	0
Exploratory dry hole costs	41,297	0	0
Loss on extinguishment of debt	24,747	0	0
Accretion of asset retirement obligations	6,306	7,080	6,293
Non-cash stock-based compensation	19,353	19,502	20,068
Gain on sale of properties and equipment	(766)	(43)	(385)
Amortization of debt discount and issuance costs	12,907	16,167	7,040
Deferred income taxes	(203,685)	(137,249)	(41,415)
Other	2,265	2,603	(3,216)
Total adjustments to net loss to reconcile to net cash from operating activities:	709,573	712,715	489,054
Changes in current assets and liabilities:
Accounts receivable	(60,546)	(32,627)	24,815
Other assets	(5,886)	2,303	(2,264)
Production tax liability	31,316	9,223	(1,629)
Accounts payable and accrued expenses	31,378	(162)	(30,310)
Funds held for distribution	24,472	36,510	2,699
Asset retirement obligations	(10,176)	(4,109)	(4,458)
Other liabilities	(4,064)	8,338	1,446
Total changes in assets and liabilities	6,494	19,476	(9,701)
Net cash from operating activities	588,563	486,263	411,073
Cash flows from investing activities:
Capital expenditures for development of crude oil and natural gas properties	(737,208)	(436,884)	(599,546)
Capital expenditures for other properties and equipment	(5,094)	(3,464)	(5,122)
Acquisition of crude oil and natural gas properties, including settlement adjustments and deposit for pending acquisition	(15,628)	(1,073,723)	0
Proceeds from sale of properties and equipment	9,991	4,945	405
Sale of promissory note	40,203	0	0
Restricted cash	(9,250)	0	0
Sale of short-term investments	49,890	0	0
Purchase of short-term investments	(49,890)	0	0
Net cash from investing activities	(716,986)	(1,509,126)	(604,263)
Cash flows from financing activities:
Proceeds from issuance of equity, net of issuance costs	0	855,074	202,851
Proceeds from issuance of senior notes	592,366	392,172	0
Proceeds from issuance of convertible senior notes	0	193,935	0
Proceeds from revolving credit facility	0	85,000	397,000
Repayment of revolving credit facility	0	(122,000)	(416,000)
Redemption of senior notes	(519,375)	0	0
Redemption of convertible notes	0	(115,000)	0
Payment of debt issuance costs	(50)	(15,556)	(974)
Purchase of treasury shares	(6,672)	(6,935)	(6,055)
Other	(1,271)	(577)	1,152
Net cash from financing activities	64,998	1,266,113	177,974
Net change in cash and cash equivalents	(63,425)	243,250	(15,216)
Cash and cash equivalents, end of year	180,675	244,100	850
Cash and cash equivalents, beginning of year	244,100	850	16,066
Cash payments (receipts) for:
Interest, net of capitalized interest	69,880	43,406	45,642
Income taxes	(13,925)	167	10,049
Non-cash investing activities:
Issuance of common stock for acquisition of crude oil and natural gas properties	0	690,702	0
Change in accounts payable related to capital expenditures	50,761	(40,448)	(45,230)
Change in asset retirement obligation, with a corresponding change to crude oil and natural gas properties, net of disposal	839	4,894	14,030
Purchase of properties and equipment under capital leases	$ 3,497	$ 1,404	$ 1,601