Earnings Per Common Unit (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Common Unit
Net (loss) income attributable to the Partnership's unitholders									$ 38,077	$ 220,402	$ 60,695
Less: Income allocable to phantom units									(2,342)	(2,142)	(1,749)
Income available for common unitholders-basic									35,735	218,260	58,946
Add: Income allocable to phantom units and DER expense									2,419	2,183
Income available for common unitholders-diluted									38,154	220,443	58,946
Weighted average common units outstanding-basic (in units)									138,409	109,979	78,466
Potential common units (Class B and phantom units)									22,034	20,669	153
Weighted average common units outstanding-diluted (in units)									160,443	130,648	78,619
Net income attributable to the Partnership's common unitholders per common unit
Basic (in dollars per unit)	$ (0.05)	$ (0.17)	$ 0.63	$ (0.12)	$ 0.26	$ (0.13)	$ 1.74	$ 0.16	$ 0.26	$ 1.98	$ 0.75
Diluted (in dollars per unit)	$ (0.05)	$ (0.17)	$ 0.55	$ (0.12)	$ 0.22	$ (0.13)	$ 1.47	$ 0.14	$ 0.24	$ 1.69	$ 0.75
Class B Units
Earnings Per Common Unit
Net (loss) income attributable to the Partnership's unitholders									$ 0	$ 0	$ 0
Net income attributable to the Partnership's common unitholders per common unit
Basic (in dollars per unit)									$ 0.00	$ 0.00	$ 0.00
Diluted (in dollars per unit)									$ 0.00	$ 0.00	$ 0.00