Partners' Capital and Distributions (Distributions) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Distribution Made to Limited Partner [Line Items]
Per Unit Amount		$ 0.6400	$ 0.6250	$ 0.6100	$ 0.5950	$ 0.5800	$ 0.5650	$ 0.5500	$ 0.5350
Distribution Made to Limited Partner, Cash Distributions Paid		$ 70,387	$ 68,737	$ 60,774	$ 56,542	$ 54,112	$ 50,114	$ 48,783	$ 47,453
Distribution Made to Limited Partner, Distribution Date		Nov. 13, 2015	Aug. 14, 2015	May 15, 2015	Feb. 13, 2015	Nov. 14, 2014	Aug. 14, 2014	May 15, 2014	Feb. 14, 2014
Scenario, Forecast [Member]
Distribution Made to Limited Partner [Line Items]
Per Unit Amount	$ 0.6550
Distribution Made to Limited Partner, Cash Distributions Paid	$ 72,036
Distribution Made to Limited Partner, Distribution Date	Feb. 12, 2016