CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 117,231	$ 105,720
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, depletion and amortization	82,128	135,100
Deferred income tax expense	64,287	53,289
Loss on sale of assets	41,049	223
Exploratory dry hole cost	(60)	2,842
Gain on derivative instruments	(5,577)	(33,384)
Net cash paid in settlement of derivative instruments	(26,131)	(1,524)
Loss on equity method investments	994	1,283
Amortization of debt issuance costs	1,195	1,189
Stock-based compensation and other	5,184	8,283
Changes in assets and liabilities:
Accounts receivable, net	50,216	(1,738)
Income taxes	(24,646)	10,534
Inventories	(4,309)	1,209
Other current assets	1,023	1,170
Accounts payable and accrued liabilities	(14,169)	151
Interest payable	(15,318)	(15,388)
Other assets and liabilities	(337)	419
Net cash provided by operating activities	272,760	269,378
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures	(156,257)	(208,384)
Proceeds from sale of assets	646,545	374
Investment in equity method investments	(35,418)	(7,742)
Net cash provided by (used in) investing activities	454,870	(215,752)
CASH FLOWS FROM FINANCING ACTIVITIES
Treasury stock repurchases	(207,134)	0
Dividends paid	(27,647)	(9,306)
Tax withholdings on vesting of stock awards	(7,968)	(5,414)
Other	0	37
Net cash used in financing activities	(242,749)	(14,683)
Net increase in cash and cash equivalents	484,881	38,943
Cash and cash equivalents, beginning of period	480,047	498,542
Cash and cash equivalents, end of period	$ 964,928	$ 537,485