Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	$ 97,751		$ 78,674
Restricted cash	408		398
Commodity derivatives, net (a)	967	[1]	70,600	[1]
Convertible preferred securities	25,720	[2]	17,200	[2]
Other assets and liabilities	9,984	[3]	5,704	[3]
Total	134,830		172,576
Level 1
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	97,751		78,674
Restricted cash	408		398
Commodity derivatives, net (a)	50,777	[1]	46,966	[1]
Convertible preferred securities	0	[2]	0	[2]
Other assets and liabilities	10,143	[3]	7,813	[3]
Total	159,079		133,851
Level 2
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	0		0
Restricted cash	0		0
Commodity derivatives, net (a)	(49,810)	[1]	23,634	[1]
Convertible preferred securities	0	[2]	0	[2]
Other assets and liabilities	(159)	[3]	(2,109)	[3]
Total	(49,969)		21,525
Level 3
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	0		0
Restricted cash	0		0
Commodity derivatives, net (a)	0	[1]	0	[1]
Convertible preferred securities	25,720	[2]	17,200	[2]
Other assets and liabilities	0	[3]	0	[3]
Total	$ 25,720		$ 17,200

[1] Includes associated cash posted/received as collateral

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

[3] Included in other assets and liabilities is interest rate and foreign currency derivatives, swaptions (Level 2) and deferred compensation assets