Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified								9 Months Ended
	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012		Sep. 30, 2013 Convertible Preferred Stock [Member] Level 3	Sep. 30, 2013 Market Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Level 3	Sep. 30, 2013 Income Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Level 3	Sep. 30, 2013 Minimum [Member] Market Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Level 3	Sep. 30, 2013 Minimum [Member] Income Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Level 3	Sep. 30, 2013 Maximum [Member] Market Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Level 3	Sep. 30, 2013 Maximum [Member] Income Approach Valuation Technique [Member] Convertible Preferred Stock [Member] Level 3	Sep. 30, 2013 Level 1		Dec. 31, 2012 Level 1		Sep. 30, 2012 Level 1		Sep. 30, 2013 Level 2		Dec. 31, 2012 Level 2		Sep. 30, 2012 Level 2		Sep. 30, 2013 Level 3		Dec. 31, 2012 Level 3		Sep. 30, 2012 Level 3
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Multiple								6.60		5.50		7.00
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	90,093		78,674		39,904									90,093		78,674		39,904		0		0		0		0		0		0
Restricted cash	164		398		160									164		398		160		0		0		0		0		0		0
Commodity derivatives, net	7,525		70,600		129,132	[1]								62,560		46,966		15,619	[1]	(55,035)		23,634		113,513	[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	8,494	[3]	5,704	[3]	5,549	[3]								9,539	[3]	7,813	[3]	7,515	[3]	(1,045)	[3]	(2,109)	[3]	(1,966)	[3]	0	[3]	0	[3]	0	[3]
Total	$ 123,986		$ 172,596		$ 192,095									$ 162,356		$ 133,851		$ 63,198		$ (56,080)		$ 21,525		$ 111,547		$ 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 are interest rate and foreign currency derivatives, swaptions and deferred compensation assets.