Partners' Capital and Distributions Partners' Capital and Distributions (Distributions) (Details) - USD ($) $ / shares in Units, $ in Thousands													12 Months Ended
	Nov. 14, 2017	Aug. 14, 2017	May 15, 2017	Feb. 14, 2017	Nov. 14, 2016	Aug. 12, 2016	May 13, 2016	Feb. 12, 2016	Nov. 13, 2015	Aug. 14, 2015	May 15, 2015	Feb. 13, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Partners' Capital Notes [Abstract]
Partners' Capital Account, Distribution Per Unit of Limited Partner Interest	$ 0.9050	$ 0.8900	$ 0.8725	$ 0.8550	$ 0.83750	$ 0.8200	$ 0.8025	$ 0.7850	$ 0.7625	$ 0.7400	$ 0.7175	$ 0.6950	$ 3.5225	$ 3.245	$ 2.915
Limited Partners' Capital Account, Distribution Amount	$ 206,362	$ 202,942	$ 198,951	$ 194,961	$ 190,769	$ 186,783	$ 182,797	$ 178,808	$ 173,413	$ 168,296	$ 163,178	$ 158,061	$ 803,216	$ 739,157	$ 662,948