CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement of Cash Flows [Abstract]
Net income	$ 16,727,000	$ 26,336,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	198,709,000	169,570,000
Exploratory dry hole expense	159,000	606,000
Impairment of properties	21,521,000	142,000
Share-based Compensation	8,113,000	4,350,000
Change in Net Profits Plan liability	(1,925,000)	3,939,000
Unrealized derivative loss	42,364,000	7,652,000
Amortization of debt discount and deferred financing costs	1,077,000	3,665,000
Deferred income taxes	10,280,000	15,288,000
Other	1,032,000	(2,580,000)
Changes in current assets and liabilities:
Accounts receivable	(22,164,000)	(13,967,000)
Refundable income taxes	251,000	3,006,000
Prepaid expenses and other	354,000	(3,003,000)
Accounts payable and accrued expenses	5,794,000	(26,951,000)
Net cash provided by operating activities	282,292,000	188,053,000
Cash flows from investing activities:
Net proceeds from sale of oil and gas properties	4,307,000	1,679,000
Capital expenditures	(381,185,000)	(335,015,000)
Other	(2,025,000)	1,550,000
Net cash used in investing activities	(378,903,000)	(331,786,000)
Cash flows from financing activities:
Proceeds from credit facility	223,500,000	26,000,000
Repayment of credit facility	(133,500,000)	(2,000,000)
Proceeds from sale of common stock	772,000	1,038,000
Other	0	(213,000)
Net cash provided by financing activities	90,772,000	24,825,000
Net change in cash and cash equivalents	(5,839,000)	(118,908,000)
Cash and cash equivalents at end of period	87,000	286,000
Supplemental schedule of additional cash flow information and noncash investing and financing activities:
Cash paid for interest	(24,721,000)	(11,729,000)
Net cash refunded for income taxes	165,000	3,397,000
Dividends, Common Stock	3,300,000	3,200,000
Capital Expenditures Incurred but Not yet Paid	$ 202,800,000	$ 199,600,000