Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Current Assets
Cash and cash equivalents	$ 1,321	$ 2,523
Short-term investments	18,000	0
Accounts receivable, net of allowance for doubtful accounts of $681 and $696 at September 30, 2014 and December 31, 2013, respectively	185,342	136,334
Inventories	14,373	11,130
Assets held for sale with prior period comparable	0	1,242,872
Deferred income taxes	8,085	21,250
Derivative instruments	30,195	17,463
Prepayments and other	31,205	9,989
Total current assets	288,521	1,441,561
Oil and natural gas properties, successful efforts method
Proved properties	7,635,488	6,695,400
Unproved properties	158,500	168,975
Less accumulated depreciation, depletion and amortization	2,336,114	1,776,802
Oil and natural gas properties, net	5,457,874	5,087,573
Other property and equipment, net	43,355	30,515
Total property, plant and equipment, net	5,501,229	5,118,088
Other Assets
Other postretirement assets	4,566	8,894
Noncurrent derivative instruments	5,758	5,439
Other assets	32,896	48,230
TOTAL ASSETS	5,832,970	6,622,212
Current Liabilities
Long-term debt due within one year	0	60,000
Notes payable to banks	0	489,000
Accounts payable	110,955	78,178
Accrued taxes	227,180	8,201
Accrued wages and benefits	39,515	27,036
Accrued capital costs	131,792	93,623
Revenue and royalty payable	65,271	51,519
Liabilities related to assets held for sale with prior period comparable	0	831,570
Derivative instruments	808	30,302
Other	17,917	21,796
Total current liabilities	593,438	1,691,225
Deferred Credits and Other Liabilities
Long-term debt	632,458	1,093,541
Asset retirement obligations	115,431	108,533
Pension liabilities	41,264	47,484
Deferred income taxes	1,074,690	807,614
Noncurrent derivative instruments	640	398
Other long-term liabilities	13,801	15,398
Total liabilities	2,471,722	3,764,193
Commitments and Contingencies
Shareholders’ Equity
Preferred stock, cumulative, $0.01 par value, 5,000,000 shares authorized	0	0
Common shareholders’ equity
Common stock, $0.01 par value; 150,000,000 shares authorized; 76,098,344 shares and 75,574,156 shares issued at September 30, 2014 and December 31, 2013, respectively	761	756
Premium on capital stock	561,826	523,711
Retained earnings	2,946,390	2,476,616
Accumulated other comprehensive income (loss), net of tax
Unrealized gain on hedges, net	3,618	13,362
Pension and postretirement plans	(26,313)	(32,245)
Interest rate swap	0	(1,184)
Deferred compensation plan	3,320	3,259
Treasury stock, at cost; 2,986,201 shares and 2,967,999 shares at September 30, 2014 and December 31, 2013, respectively	(128,354)	(126,256)
Total shareholders’ equity	3,361,248	2,858,019
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 5,832,970	$ 6,622,212