Earnings Per Common Unit (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Common Unit
Net (loss) income attributable to the Partnership's unitholders	$ (23,604)	$ (14,340)	$ 44,637	$ 188,588
Less: Income allocable to phantom units	618	541	1,718	1,595
(Loss) income available for common unitholders - basic	(24,222)	(14,881)	42,919	186,993
Add: Income allocable to phantom units and DER expense			1,774	1,627
(Loss) income available for common unitholders - diluted	(24,222)	(14,881)	44,693	188,620
Weighted average common units outstanding - basic (in units)	142,352,000	113,994,000	134,115,000	105,916,000
Potential common shares (Class B and phantom units)			19,340,000	20,679,000
Weighted average common units outstanding - diluted (in units)	142,352,000	113,994,000	153,455,000	126,595,000
Net (loss) income attributable to the Partnership's common unitholders per common unit
Basic (in dollars per unit)	$ (0.17)	$ (0.13)	$ 0.32	$ 1.77
Diluted (in dollars per unit)	$ (0.17)	$ (0.13)	$ 0.29	$ 1.49
Anti-dilutive units (in units)	16,760	20,641
Class B Units
Earnings Per Common Unit
Net (loss) income attributable to the Partnership's unitholders	$ 0	$ 0	$ 0	$ 0
Net (loss) income attributable to the Partnership's common unitholders per common unit
Basic (in dollars per unit)	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Diluted (in dollars per unit)	$ 0.00	$ 0.00	$ 0.00	$ 0.00