CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012
Statement of Cash Flows [Abstract]
Net income (loss)	$ 163,939,000		$ 12,889,000
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on divestiture activity	(510,000)		(31,246,000)
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	620,232,000		523,610,000
Exploratory dry hole expense	5,878,000		18,551,000
Impairment of proved properties	61,706,000		38,523,000
Abandonment and impairment of unproved properties	8,459,000		11,296,000
Stock-based compensation expense	25,495,000		21,731,000
Change in Net Profits Plan liability	(6,423,000)		(17,342,000)
Derivative (gain) loss	(14,685,000)	[1]	(40,040,000)	[1]
Derivative cash settlement gain	12,715,000	[2]	32,803,000	[2]
Amortization of debt discount and deferred financing costs	3,914,000		5,692,000
Deferred income taxes	98,619,000		7,305,000
Plugging and abandonment	(7,453,000)		(1,804,000)
Other	2,929,000		906,000
Changes in current assets and liabilities:
Accounts receivable	(45,209,000)		(18,682,000)
Refundable income taxes	510,000		2,339,000
Prepaid expenses and other	(2,971,000)		(6,203,000)
Accounts payable and accrued expenses	72,704,000		30,766,000
Net Cash Provided by Operating Activities	1,000,869,000		653,586,000
Cash flows from investing activities:
Net proceeds from sale of oil and gas properties	20,498,000		48,663,000
Capital expenditures	(1,121,355,000)		(1,126,755,000)
Acquisition of proved and unproved oil and gas properties	(62,007,000)		(5,604,000)
Other	(3,509,000)		0
Net cash used in investing activities	(1,166,373,000)		(1,083,696,000)
Cash flows from financing activities:
Proceeds from credit facility	976,500,000		1,234,500,000
Repayment of credit facility	(1,288,500,000)		(1,006,500,000)
Deferred financing costs related to credit facility	(3,444,000)		0
Net proceeds from 5.0% Senior Notes Due 2024	490,274,000		0
Net proceeds from 6.50% Senior Notes Due 2023	0		392,223,000
Repayment of 3.50% Convertible Notes	0		(287,500,000)
Proceeds from sale of common stock	4,450,000		3,421,000
Dividends paid	(3,314,000)		(3,208,000)
Net share settlement from issuance of stock awards	(16,203,000)		(21,605,000)
Other	(9,000)		(231,000)
Net cash provided by financing activities	159,754,000		311,100,000
Net change in cash and cash equivalents	(5,750,000)		(119,010,000)
Cash and cash equivalents at beginning of period	5,926,000		119,194,000
Cash and cash equivalents at ending of period	176,000		184,000
Supplemental schedule of additional cash flow information and noncash investing and financing activities:
Cash paid for interest, net of capitalized interest	(59,841,000)		(41,413,000)
Net cash refunded for income taxes	259,000		1,583,000
Capital expenditures incurred but not yet paid	238,700,000		213,600,000
Dividends, Common Stock	$ 3,300,000		$ 3,300,000

[1] (2) Total derivative (gain) loss is reported in the derivative gain line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.

[2] (1) Derivative cash settlement (gain) loss is reported in the derivative cash settlement gain line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.