CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
ASSETS
Cash and cash equivalents	$ 282,248	$ 5,926
Accounts receivable (Note 2)	318,371	254,805
Refundable income taxes	4,630	3,364
Prepaid expenses and other	9,944	30,017
Derivative asset	21,559	37,873
Deferred income taxes	10,749	8,579
Total current assets	647,501	340,564
Land	1,857	1,845
Proved oil and gas properties	5,637,462	5,401,684
Less - accumulated depletion, depreciation, and amortization	(2,583,698)	(2,376,170)
Unproved oil and gas properties	271,100	175,287
Wells in progress	279,654	273,928
Materials inventory, at lower of cost or market	15,950	13,444
Oil and gas properties held for sale, net of accumulated depletion, depreciation and amortization of $7,390 in 2013 and $20,676 in 2012	19,072	33,620
Other property and equipment, net of accumulated depreciation of $28,775 in 2013 and $22,442 in 2012	218,395	153,559
Total property and equipment, net	3,859,792	3,677,197
Derivative asset	30,951	16,466
Restricted cash	96,713	86,773
Other noncurrent assets	70,208	78,529
Total other noncurrent assets	197,872	181,768
Total Assets	4,705,165	4,199,529
LIABILITIES
Accounts payable and accrued expenses (note 2)	606,751	525,627
Derivative liabilities	26,380	8,999
Other current liabilities	6,000	6,920
Total current liabilities	639,131	541,546
Revolving credit facility	0	340,000
Senior Notes (note 5)	1,600,000	1,100,000
Asset retirement obligation	115,659	112,912
Asset retirement obligation associated with oil and gas properties held for sale	3,033	1,393
Net Profits Plan liability	56,985	78,827
Deferred income taxes; Net, non-current	650,125	537,383
Derivative liabilities	4,640	6,645
Other noncurrent liabilities	28,771	66,357
Total noncurrent liabilities	2,459,213	2,243,517
Commitments and contingencies (note 6)
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value - authorized: 200,000,000 shares; issued: 67,078,853 shares in 2013 and 66,245,816 shares in 2012; outstanding, net of treasury shares: 67,056,441 shares in 2013 and 66,195,235 shares in 2012	671	662
Additional paid-in capital	257,720	233,642
Treasury stock, at cost: 22,412 shares in 2013 and 50,581 shares in 2012	(823)	(1,221)
Retained earnings	1,354,669	1,190,397
Accumulated other comprehensive loss	(5,416)	(9,014)
Total stockholders' equity	1,606,821	1,414,466
Total Liabilities and Stockholders' Equity	$ 4,705,165	$ 4,199,529