Fair Value Measurements (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents		$ 8,943	$ 269	$ 13,364
Restricted cash		941	429	895
Commodity derivatives, net	[1]	(1,949)	25,885	69,163
Convertible preferred securities	[2]	13,300	13,300	16,950
Other assets and liabilities	[3]	8,966	8,203	8,799
Total		30,201	48,086	109,171
Level 1
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents		8,943	269	13,364
Restricted cash		941	429	895
Commodity derivatives, net	[1]	(6,960)	72,868	111,184
Convertible preferred securities	[2]	0	0	0
Other assets and liabilities	[3]	11,531	10,869	10,662
Total		14,455	84,435	136,105
Level 2
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents		0	0	0
Restricted cash		0	0	0
Commodity derivatives, net	[1]	5,011	(46,983)	(42,021)
Convertible preferred securities	[2]	0	0	0
Other assets and liabilities	[3]	(2,565)	(2,666)	(1,863)
Total		2,446	(49,649)	(43,884)
Level 3
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents		0	0	0
Restricted cash		0	0	0
Commodity derivatives, net	[1]	0	0	0
Convertible preferred securities	[2]	13,300	13,300	16,950
Other assets and liabilities	[3]	0	0	0
Total		$ 13,300	$ 13,300	$ 16,950

[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 deferred compensation assets (Level 1) and interest rate derivatives (Level 2)