CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Liabilities
Cash and cash equivalents	$ 176	$ 5,926
Accounts receivable	291,197	254,805
Refundable income taxes	2,716	3,364
Prepaid expense and other	30,340	30,017
Derivative asset	58,071	37,873
Deferred income taxes	13,136	8,579
Total current assets	395,636	340,564
Land	1,857	1,845
Proved oil and gas properties	5,922,411	5,401,684
Less - accumulated depletion, depreciation, and amortization	(2,737,774)	(2,376,170)
Unproved oil and gas properties	234,741	175,287
Wells in progress	290,289	273,928
Materials inventory, at lower of cost or market	14,012	13,444
Oil and gas properties held for sale net of accumulated depletion, depreciation and amortization of $55,348 in 2013 and 20,676 in 2012	87,310	33,620
Other property and equipment, net of accumulated depreciation of $25,542 in 2013 and $22,442 in 2012	176,243	153,559
Total property and equipment, net	3,989,089	3,677,197
Derivative asset	28,798	16,466
Restricted cash	94,311	86,773
Other noncurrent assets	82,834	78,529
Total other noncurrent assets	205,943	181,768
Total Assets	4,590,668	4,199,529
Liabilities
Accounts payable and accrued expenses	577,452	525,627
Derivative liability	4,748	8,999
Other current liabilities	6,000	6,920
Total current liabilities	588,200	541,546
Revolving credit facility	28,000	340,000
6.625% Senior Notes Due 2019	350,000	350,000
6.50% Senior Notes Due 2021	350,000	350,000
6.50% Senior Notes Due 2023	400,000	400,000
5.0% Senior Notes Due 2024	500,000	0
Asset retirement obligation	118,383	112,912
Asset retirement obligation associated with oil and gas properties held for sale	4,617	1,393
Net Profits Plan liability	71,464	78,827
Deferred income taxes	598,662	537,383
Derivatives liability	1,525	6,645
Other noncurrent liabilities	52,914	66,357
Total noncurrent liabilities	2,475,565	2,243,517
Commitments and contingencies (note 6)
Stockholders' equity:
Common stock, $0.01 par value - authorized: 200,000,000 shares; issued: 66,412,394 shares in 2013 and 66,245,816 shares in 2012; outstanding, net of treasury shares: 66,389,982 shares in 2013 and 66,195,235 shares in 2012	664	662
Additional paid-in-capital	254,940	233,642
Treasury stock, at cost: 22,412 shares in 2013 and 50,581 in 2012	(823)	(1,221)
Retained earnings	1,280,332	1,190,397
Accumulated other comprehensive loss	(8,210)	(9,014)
Total stockholders' equity	1,526,903	1,414,466
Total Liabilities and Stockholders' Equity	$ 4,590,668	$ 4,199,529