Earnings Per Common Unit (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings (Loss) Per Common Unit
Net income attributable to the Partnership's unitholders	$ 83,699	$ 186,908	$ 68,241	$ 202,928
Less: Income allocable to phantom units	554	1,209	1,100	1,391
Income available for common unitholders - basic	83,145	185,699	67,141	201,537
Add: Income allocable to phantom units and DER expense	569	1,218	1,135	1,414
Income available for common unitholders - diluted	83,714	186,917	68,276	202,951
Weighted average common units outstanding - basic (in units)	131,227	106,825	129,928	101,833
Potential common shares (Class B and phantom units)	20,639	20,643	20,652	20,698
Weighted average common units outstanding - diluted (in units)	151,866	127,468	150,580	122,531
Net income attributable to the Partnership's common unitholders per common unit
Basic (in dollars per unit)	$ 0.63	$ 1.74	$ 0.52	$ 1.98
Diluted (in dollars per unit)	$ 0.55	$ 1.47	$ 0.45	$ 1.66
Class B Units
Earnings (Loss) Per Common Unit
Net income attributable to the Partnership's unitholders	$ 0	$ 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	$ 0.00
Diluted (in dollars per unit)	$ 0	$ 0	$ 0	$ 0