Net Income (Loss) Per Limited Partner Unit (Details 2) (USD $)	0 Months Ended	3 Months Ended		0 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended
	Feb. 14, 2013	Mar. 31, 2013	Dec. 31, 2012	Mar. 02, 2012 Seller	Mar. 31, 2012 Seller	Mar. 31, 2012 Weighted average	Mar. 31, 2012 Alliance	Mar. 02, 2012 Alliance
Net Income Per Limited Partner Unit
Issuance of common units in connection with acquisition							5,850,000
General partner ownership interest (as a percent)		0.83%				0.97%
Adjustment in purchase price due to timing of transaction								$ 1,900,000
Period of actual unit ownership considered for purchase price adjustment				31 days			31 days
Period in quarter considered for actual unit ownership				91 days			91 days
Cash distribution to common units	$ 16,346,000				$ 1,000,000
Quarterly cash distributions paid (in dollars per unit)	$ 0.57		$ 0.57		$ 0.50