Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income (loss)	$ (13,139)	$ 46,146
Net income (loss)	(13,139)	46,146
Adjustments to net income (loss) to reconcile to net cash provided by operating activities:
Net change in fair value of unsettled derivatives	21,202	(80,153)
Depreciation, depletion, and amortization	126,788	109,316
Impairment of properties and equipment	33,188	2,193
Accretion of asset retirement obligations	1,288	1,768
Non-cash stock-based compensation	5,261	4,454
(Gain) loss on sale of properties and equipment	1,432	(160)
Amortization of debt discount and issuance costs	3,246	3,184
Deferred income taxes	(4,809)	26,280
Other	515	722
Changes in assets and liabilities	30,177	25,750
Net cash from operating activities	205,149	139,500
Cash flows from investing activities:
Capital expenditures for development of crude oil and natural gas properties	(196,917)	(129,826)
Capital expenditures for other properties and equipment	(1,066)	(821)
Acquisition of crude oil and natural gas properties, including settlement adjustments	(180,825)	6,181
Proceeds from sale of properties and equipment	20	737
Proceeds from divestiture	39,023	0
Restricted cash	1,249	0
Purchases of short-term investments	0	(49,890)
Net cash from investing activities	(338,516)	(173,619)
Cash flows from financing activities:
Proceeds from revolving credit facility	35,000	0
Repayment of revolving credit facility	(35,000)	0
Purchase of treasury shares	(2,255)	(2,017)
Other	(379)	(340)
Net cash from financing activities	(2,634)	(2,357)
Net change in cash, cash equivalents, and restricted cash	(136,001)	(36,476)
Cash, cash equivalents, and restricted cash, beginning of period	189,925	244,100
Cash, cash equivalents, and restricted cash, end of period	53,924	207,624
Cash payments (receipts) for:
Interest, net of capitalized interest	12,343	13,224
Income taxes	193	(39)
Non-cash investing and financing activities:
Change in accounts payable related to purchases of properties and equipment	51,093	69,604
Change in asset retirement obligation, with a corresponding change to crude oil and natural gas properties, net of disposals	5,354	1,233
Purchase of properties and equipment under capital leases	$ 348	$ 1,190