Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Current assets
Cash	$ 56,478	$ 4,951	$ 7,436	$ 13,146
Marketable Securities, Current	129,812	0
Cash, Cash Equivalents, and Short-term Investments	186,290	4,951
Accounts receivable - net of allowance for doubtful accounts	55,242	64,149
Derivative assets at fair value	86,003	113,367
Other current assets	22,413	25,046
Total current assets	349,948	207,513
Property, plant and equipment - net
Oil and gas properties, full cost method (including unevaluated costs of $291,147 and $307,267, respectively)	629,684	780,960
Property, Plant and Equipment, Other, Net	233,248	248,098
Property, plant and equipment, net of accumulated depletion and depreciation	862,932	1,029,058
Derivative assets at fair value	75,328	105,270
Other assets	43,405	39,947
Total assets	1,331,613	1,381,788
Current liabilities
Current portion of long-term debt	0	0
Accounts payable	12,745	37,131
Accrued liabilities	102,913	130,660
Total current liabilities	115,658	167,791
Long-term debt	1,926,167	2,063,206
Partnership liability	132,732	130,912
Asset retirement obligations	99,160	115,949
Derivative liabilities at fair value	3,172	17,485
Other liabilities	19,242	19,242
Commitments and contingencies (Note 8)
Stockholders' equity
Preferred stock, par value $0.01, 10,000,000 shares authorized, none outstanding	0	0
Common stock, $0.01 par value, 400,000,000 shares authorized, and 183,685,021 and 179,015,118 shares issued, respectively	1,837	1,790
Paid in capital in excess of par value	765,815	751,394
Treasury stock of 6,545,651 and 5,921,102 shares, respectively	(50,967)	(49,495)
Accumulated other comprehensive income	123,379	161,493
Retained deficit	(1,804,582)	(1,997,979)
Total stockholders' equity	(964,518)	(1,132,797)
Total liabilities and stockholders' equity	$ 1,331,613	$ 1,381,788