Summary of Significant Accounting Policies (Details 10) (USD $)	0 Months Ended														3 Months Ended							12 Months Ended	0 Months Ended					1 Months Ended	12 Months Ended		1 Months Ended
	Feb. 05, 2014	Jan. 22, 2014	Nov. 14, 2013	Aug. 14, 2013	May 15, 2013	Feb. 14, 2013	Nov. 14, 2012	Aug. 14, 2012	May 14, 2012	Feb. 14, 2012	Nov. 14, 2011	Aug. 12, 2011	May 13, 2011	Feb. 14, 2011	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2013	Jan. 22, 2014 General Partner Interest	Oct. 23, 2013 General Partner Interest	Jul. 23, 2013 General Partner Interest	Apr. 24, 2013 General Partner Interest	Mar. 02, 2012 Seller	Mar. 31, 2012 Seller	Dec. 31, 2012 Weighted average	Dec. 31, 2011 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				5,850,000
General partner ownership interest (as a percent)																						0.83%							0.86%	1.09%
Adjustment in purchase price due to timing of transaction																																$ 1,900,000
Period of actual unit ownership considered for purchase price adjustment																											31 days
Period in quarter considered for actual unit ownership																											91 days
Cash distribution to common units	$ 17,900,000		$ 17,425,000	$ 16,975,000	$ 16,796,000	$ 16,346,000	$ 15,019,000	$ 14,781,000	$ 13,986,000	$ 11,028,000	$ 11,028,000	$ 11,028,000	$ 11,028,000	$ 9,691,000														$ 1,000,000
Quarterly cash distributions paid (in dollars per unit)			$ 0.6000	$ 0.5875	$ 0.5825	$ 0.5700	$ 0.5325	$ 0.5250	$ 0.5000	$ 0.5000	$ 0.5000	$ 0.5000	$ 0.5000	$ 0.5000	$ 0.0000	$ 0.60	$ 0.5875	$ 0.5825	$ 0.57	$ 0.5325	$ 0.5250	$ 0.50						$ 0.50
Quarterly cash distribution declared (in dollars per unit)		$ 0.6125																					$ 0.6125	$ 0.60	$ 0.5875	$ 0.5825	$ 0.50