Partners' Capital and Distributions (Distributions) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Partners' Capital Notes [Abstract]
Date Paid	Feb. 14, 2013	Nov. 14, 2012	Aug. 14, 2012	May 15, 2012	Feb. 14, 2012	Nov. 14, 2011	Aug. 12, 2011	May 13, 2011	Feb. 14, 2011
Per Unit Amount	$ 0.4850	$ 0.4725	$ 0.4600	$ 0.4500	$ 0.4400	$ 0.4275	$ 0.4150	$ 0.4075	$ 0.4000	$ 0.4850	$ 0.4400	$ 0.4000
Total Amount	$ 39,390	$ 38,375	$ 36,563	$ 35,768	$ 31,677	$ 30,777	$ 29,878	$ 26,343	$ 25,846	$ 142,383	$ 112,844	$ 70,359