CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Operating Activities
Net income (loss)	$ (945,731)	$ 568,032	$ 204,554
Income from discontinued operations	0	(468,389)	(62,673)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	593,789	548,564	452,876
Asset impairment	1,292,308	416,801	13,906
Accretion of discount on asset retirement obligations	7,108	7,608	6,995
Deferred income taxes	(539,735)	302,890	118,600
Change in derivative fair value	233,315	(346,646)	48,029
(Gain) loss on sale of assets	(28,077)	55	(89)
Stock-based compensation expense	8,028	11,332	13,621
Exploration, including dry holes	7,097	9,325	2,102
Discontinued operations	0	91,510	109,318
Other, net	35,641	4,166	12,284
Net change in:
Accounts receivable	117,486	4,812	23,785
Inventories	(655)	(3,121)	10,817
Accounts payable	(46,283)	18,695	(52,946)
Accrued taxes/income tax receivable	(4,791)	(488,980)	4,092
Pension and other postretirement benefit contributions	(24,848)	(12,483)	(5,677)
Other current assets and liabilities	9,940	41,312	27,783
Net cash provided by operating activities	714,592	705,483	927,377
Investing Activities
Additions to oil and natural gas properties	(1,154,373)	(1,264,059)	(1,109,365)
Acquisitions, net of cash acquired	(87,410)	(70,730)	(31,331)
Proceeds from asset sales and sale of Alabama Gas Corporation	394,521	1,347,725	160,986
Purchase of short-term investments	(919,000)	(473,000)	(310,000)
Sale of short-term investments	919,000	473,000	310,000
Discontinued operations	0	(51,850)	(73,341)
Other, net	0	0	(559)
Net cash used in investing activities	(847,262)	(38,914)	(1,053,610)
Financing Activities
Payment of dividends on common stock	(6,074)	(34,304)	(41,993)
Issuance of common stock, net	399,600	23,053	17,780
Purchase and retirement of shares	0	(14,913)	0
Issuance of long-term debt	0	0	600,000
Reduction of long-term debt	0	(600,000)	(350,000)
Payment of debt issuance costs	0	(10,901)	(2,740)
Net change in credit facility	(262,500)	(4,000)	(77,000)
Tax benefit on stock compensation	1,064	5,906	3,142
Discontinued operations	0	(35,113)	(27,105)
Net cash provided by (used in) financing activities	132,090	(670,272)	122,084
Net change in cash and cash equivalents	(580)	(3,703)	(4,149)
Cash and cash equivalents at beginning of period	1,852	5,555	9,704
Cash and cash equivalents at end of period	1,272	1,852	5,555
Less cash and cash equivalents of discontinued operations at end of period	0	0	(3,032)
Cash and cash equivalents	$ 1,272	$ 1,852	$ 2,523