Earnings (Loss) Per Common Unit (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings (Loss) Per Common Unit
Net (loss) income attributable to the Partnership's unitholders	$ (15,460)	$ 16,020
Less: Income allocable to phantom units	546	520
(Loss) Income available for common unitholders - basic	(16,006)	15,500
Add: Income allocable to phantom units and DER expense		535
(Loss) Income available for common unitholders - diluted	(16,006)	16,035
Weighted average common units outstanding - basic (in units)	128,615	96,840
Potential common units (Class B and phantom units)		20,753
Weighted average common units outstanding - diluted (in units)	128,615	117,593
Net (loss) income attributable to the Partnership's common unitholders per common unit
Basic (in dollars per unit)	$ (0.12)	$ 0.16
Diluted (in dollars per unit)	$ (0.12)	$ 0.14
Anti-dilutive units (in units)	20,664
Class B Units
Earnings (Loss) Per Common Unit
Net (loss) income attributable to the Partnership's unitholders	$ 0	$ 0
Net (loss) income attributable to the Partnership's common unitholders per common unit
Basic (in dollars per unit)	$ 0.00	$ 0.00
Diluted (in dollars per unit)	$ 0.00	$ 0.00