Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified																										6 Months Ended
	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012		Jun. 30, 2013 Level 1		Dec. 31, 2012 Level 1		Jun. 30, 2012 Level 1		Jun. 30, 2013 Level 2		Dec. 31, 2012 Level 2		Jun. 30, 2012 Level 2		Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member]		Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member]		Jun. 30, 2012 Fair Value, Inputs, Level 3 [Member]		Jun. 30, 2013 Convertible Preferred Stock [Member] Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2013 Market Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2013 Income Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2013 Minimum [Member] Market Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2013 Minimum [Member] Income Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2013 Maximum [Member] Market Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2013 Maximum [Member] Income Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Fair Value, Inputs, Level 3 [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Multiple																										6.6		5.5		7.0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value																									$ 17,710
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	32,272		78,674		104		32,272		78,674		104		0		0		0		0		0		0
Restricted cash	872		398		5,644		872		398		5,644		0		0		0		0		0		0
Commodity derivatives, net	57,830		70,600		96,636	[1]	79,006		46,966		48,558	[1]	(21,176)		23,634		48,078	[1]	0		0		0	[1]
Convertible preferred securities	17,710	[2]	17,220	[2]	17,350	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	17,710	[2]	17,220	[2]	17,350	[2]
Other assets and liabilities	8,111	[3]	5,704	[3]	5,160	[3]	8,837	[3]	7,813	[3]	7,182	[3]	(726)	[3]	(2,109)	[3]	(2,022)	[3]	0	[3]	0	[3]	0	[3]
Total	$ 116,795		$ 172,596		$ 124,894		$ 120,987		$ 133,851		$ 61,488		$ (21,902)		$ 21,525		$ 46,056		$ 17,710		$ 17,220		$ 17,350
Fair Value Inputs, Discount Rate																											17.00%		17.00%		17.00%

[1] Includes associated cash posted/received as collateral

[2] Recorded in “Other noncurrent assets” on the Company’s Condensed Consolidated Balance Sheets

[3] Included in other assets and liabilities is interest rate and foreign currency derivatives, swaptions and deferred compensation assets.