CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (in thousands, except share amounts) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents at beginning of period	$ 176	$ 5,926
Accounts receivable	278,125	254,805
Refundable income taxes	2,854	3,364
Prepaid expense and other	10,498	30,017
Derivative asset	43,305	37,873
Deferred income taxes	10,912	8,579
Total current assets	345,870	340,564
Land	1,857	1,845
Proved oil and gas properties	5,414,842	5,401,684
Less - accumulated depletion, depreciation, and amortization	(2,418,939)	(2,376,170)
Unproved oil and gas properties	263,662	175,287
Wells in progress	301,609	273,928
Materials inventory, at lower of cost or market	14,115	13,444
Oil and gas properties held for sale net of accumulated depletion, depreciation and amortization of $539,769 in 2013 and 20,676 in 2012	400,393	33,620
Other property and equipment, net of accumulated depreciation of $27,571 in 2013 and $22,442 in 2012	203,799	153,559
Total property and equipment, net	4,181,338	3,677,197
Derivative asset	28,659	16,466
Restricted cash	94,700	86,773
Other noncurrent assets	86,278	78,529
Total other noncurrent assets	209,637	181,768
Total Assets	4,736,845	4,199,529
Liabilities
Accounts payable and accrued expenses	601,131	525,627
Derivative liability	22,648	8,999
Other current liabilities	6,000	6,920
Total current liabilities	629,779	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	101,650	112,912
Asset retirement obligation associated with oil and gas properties held for sale	25,339	1,393
Net Profits Plan liability	72,404	78,827
Deferred income taxes	639,000	537,383
Derivatives liability	6,873	6,645
Other noncurrent liabilities	47,016	66,357
Total noncurrent liabilities	2,520,282	2,243,517
Commitments and contingencies (note 6)
Stockholders' equity:
Common stock, $0.01 par value - authorized: 200,000,000 shares; issued: 66,994,516 shares in 2013 and 66,245,816 shares in 2012; outstanding, net of treasury shares: 66,972,104 shares in 2013 and 66,195,235 shares in 2012	670	662
Additional paid-in-capital	247,165	233,642
Treasury stock, at cost: 22,412 shares in 2013 and 50,581 in 2012	(823)	(1,221)
Retained earnings	1,347,674	1,190,397
Accumulated other comprehensive loss	(7,902)	(9,014)
Total stockholders' equity	1,586,784	1,414,466
Total Liabilities and Stockholders' Equity	$ 4,736,845	$ 4,199,529