CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 159,662	$ 127,247
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, depletion and amortization	167,038	279,422
Impairment of oil and gas properties and other assets	0	68,555
Deferred income tax expense	66,976	73,394
Loss on sale of assets	40,505	1,626
Exploratory dry hole cost	51,085	2,842
Gain on derivative instruments	(1,909)	(47,190)
Net cash paid in settlement of derivative instruments	(20,312)	(319)
Loss on equity method investments	998	2,569
Amortization of debt issuance costs	2,390	2,384
Stock-based compensation and other	10,364	18,198
Changes in assets and liabilities:
Accounts receivable, net	38,939	13,713
Income taxes	12,107	(6,166)
Inventories	(12,377)	(4)
Other current assets	(1,096)	(1,776)
Accounts payable and accrued liabilities	7,168	(4,339)
Interest payable	(215)	(311)
Other assets and liabilities	25,337	101
Net cash provided by operating activities	546,660	529,946
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures	(387,271)	(393,333)
Proceeds from sale of assets	646,868	1,475
Investment in equity method investments	(62,905)	(13,626)
Net cash provided by (used in) investing activities	196,692	(405,484)
CASH FLOWS FROM FINANCING ACTIVITIES
Treasury stock repurchases	(419,654)	(68,255)
Dividends paid	(54,718)	(32,582)
Tax withholdings on vesting of stock awards	(8,033)	(5,672)
Other	0	39
Net cash used in financing activities	(482,405)	(106,470)
Net increase in cash and cash equivalents	260,947	17,992
Cash and cash equivalents, beginning of period	480,047	498,542
Cash and cash equivalents, end of period	$ 740,994	$ 516,534