Fair Value (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Commodity contracts (net)
Derivative assets and liabilities classified by the Partnership within Level 3 of the valuation hierarchy
Fair value at beginning of period	$ (2,965)	$ (14,357)
Total gain or loss (realized and unrealized) included in earnings	17,153	3,182
Settlements	(1,739)	8,210
Fair value at end of period	12,449	(2,965)
The amount of total 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	8,213	6,241
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	(53,904)	(34,936)
Total gain or loss (realized and unrealized) included in earnings	9,199	(30,827)
Settlements	10,748	11,859
Fair value at end of period	(33,957)	(53,904)
The amount of total 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	$ 8,175	$ (29,556)