Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current assets
Cash and cash equivalents	$ 89,103	$ 4,951	$ 13,146	$ 54,937
Marketable securities	166,343	0
Cash, Cash Equivalents, and Short-term Investments	255,446	4,951
Accounts receivable - net of allowance for doubtful accounts	58,645	64,149
Derivative assets at fair value	57,523	113,367
Other current assets	22,346	25,046
Total current assets	393,960	207,513
Property, plant and equipment - net
Oil and gas properties, full cost method (including unevaluated costs of $221,605 and $307,267, respectively)	640,443	780,960
Other property and equipment	220,362	248,098
Property, plant and equipment - net	860,805	1,029,058
Derivative assets at fair value	73,357	105,270
Other assets	41,604	39,947
Total assets	1,369,726	1,381,788
Current liabilities
Accounts payable	28,822	37,131
Accrued liabilities	102,850	130,660
Derivative liabilities at fair value	3,125	0
Total current liabilities	134,797	167,791
Long-term debt	1,988,946	2,063,206
Partnership liability	126,132	130,912
Asset retirement obligations	106,256	115,949
Derivative liabilities at fair value	323	17,485
Other liabilities	19,242	19,242
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 183,994,879 and 179,015,118 shares issued, respectively	1,840	1,790
Additional paid in capital	770,092	751,394
Treasury stock of 6,698,640 and 5,921,102 shares, respectively	(51,422)	(49,495)
Accumulated other comprehensive income	109,881	161,493
Retained deficit	(1,836,361)	(1,997,979)
Total stockholders' equity	(1,005,970)	(1,132,797)
Total liabilities and stockholders' equity	$ 1,369,726	$ 1,381,788