Fair Value (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Commodity contracts (net)
Derivative assets and liabilities classified by the Partnership within Level 3 of the valuation hierarchy
Fair value at beginning of period	$ 12,449	$ (2,965)
Total (loss) gain (realized and unrealized) included in earnings	3,324	(12,076)
Settlements	(3,296)	(2,409)
Fair value at end of period	12,477	(17,450)
The amount of total net gains for the period included in earnings attributable to the change in unrealized gains or losses relating to contracts still held at end of period	3,431	(14,050)
Embedded derivatives in commodity contracts (net)
Derivative assets and liabilities classified by the Partnership within Level 3 of the valuation hierarchy
Fair value at beginning of period	(33,957)	(53,904)
Total (loss) gain (realized and unrealized) included in earnings	6,532	(10,438)
Settlements	2,544	3,538
Fair value at end of period	(24,881)	(60,804)
The amount of total net gains for the period included in earnings attributable to the change in unrealized gains or losses relating to contracts still held at end of period	$ 6,675	$ (10,620)