Earnings (Loss) Per Common Unit (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings (Loss) Per Common Unit
Net income attributable to the Partnership's unitholders									$ 220,402	$ 60,695	$ 467
Less: Income allocable to phantom units									2,142	1,749	1,308
Income (loss) available for common unitholders - basic									218,260	58,946	(841)
Add: Income allocable to phantom units and DER expense									2,183
Income (loss) available for common unitholders - diluted									$ 220,443	$ 58,946	$ (841)
Weighted average common units outstanding - basic (in units)									109,979	78,466	70,128
Potential common units (Class B and phantom units)									20,669	153
Weighted average common units outstanding - diluted (in units)									130,648	78,619	70,128
Net income (loss) attributable to the Partnership's common unitholders per common unit
Basic (in dollars per unit)	$ 0.26	$ (0.13)	$ 1.74	$ 0.16	$ (0.87)	$ 1.77	$ 1.03	$ (1.13)	$ 1.98	$ 0.75	$ (0.01)
Diluted (in dollars per unit)	$ 0.22	$ (0.13)	$ 1.47	$ 0.14	$ (0.87)	$ 1.77	$ 1.03	$ (1.13)	$ 1.69	$ 0.75	$ (0.01)
Anti-dilutive units (in units)											195