Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating Activities
Net income (loss)	$ 62,884	$ (166,357)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	221,201	236,397
Asset impairment	1,489	220,025
Accretion of discount on asset retirement obligations	2,857	3,536
Deferred income taxes	36,801	(93,018)
Change in derivative fair value	(110,735)	64,159
(Gain) loss on sale of assets	298	(161,110)
Stock-based compensation expense	6,388	7,975
Exploration, including dry holes	0	16
Other, net	(3,012)	3,558
Net change in:
Accounts receivable	(31,037)	35,415
Inventories	(4,041)	(876)
Accounts payable	(4,437)	(14,181)
Accrued taxes/income tax receivable	32,334	19,259
Pension contributions	(59)	(14,546)
Other current assets and liabilities	(13,578)	(16,989)
Net cash provided by operating activities	197,353	123,263
Investing Activities
Additions to oil and natural gas properties	(466,508)	(228,204)
Acquisitions	(237,459)	(27,765)
Proceeds (payments) on the sale of assets, net	(301)	285,497
Net cash provided by (used in) investing activities	(704,268)	29,528
Financing Activities
Issuance of common stock, net	0	381,219
Taxes paid for shares withheld	(3,180)	(2,438)
Reduction of long-term debt	(7,000)	0
Net change in credit facility	131,500	(222,500)
Tax benefit on stock compensation	0	(455)
Net cash provided by financing activities	121,320	155,826
Net change in cash and cash equivalents	(385,595)	308,617
Cash and cash equivalents at beginning of period	386,093	1,272
Cash and cash equivalents at end of period	$ 498	$ 309,889