Partners' Capital and Distributions (Distributions) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2014
Partners' Capital Notes [Abstract]
Per Unit Amount	$ 0.5225	$ 0.5100	$ 0.4975	$ 0.4850	$ 0.4725	$ 0.4600	$ 0.4500	$ 0.4400		$ 0.5225	$ 0.4725		$ 0.5350
Distribution Made to Limited Partner, Cash Distributions Paid		$ 46,344	$ 42,302	$ 40,405	$ 39,390	$ 38,375	$ 36,563	$ 35,768
Distribution Made to Limited Partner, Distribution Date	Feb. 14, 2014	Nov. 14, 2013	Aug. 14, 2013	May 15, 2013	Feb. 14, 2013	Nov. 14, 2012	Aug. 14, 2012	May 15, 2012	Feb. 14, 2012
Total Amount	$ 47,453								$ 31,677	$ 168,441	$ 142,383	$ 112,844