Partners' Capital and Distributions (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended	12 Months Ended
	Jul. 27, 2016	Jul. 22, 2015	Apr. 10, 2015	Sep. 26, 2014	Jul. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Partners Capital And Distributions [Line Items]
Common units, outstanding (in shares)						117,979,218	109,979,218
Cash or stock available for distributions, percent usually distributed						100.00%
Days to distribute						45 days
Common units, issued (in shares)					10,350,000	117,979,218	109,979,218
Price per share of common units issued (in dollars per share)	$ 37.90	$ 43.77	$ 44.42	$ 50.71
Net proceeds received from sale of units, net of underwriter discounts	$ 298,452	$ 437,164	$ 198,168	$ 225,725	$ 437,200
Class A [Member]
Partners Capital And Distributions [Line Items]
Common units, issued (in shares)	8,000,000	10,350,000	4,600,000	4,600,000
Price per share of common units issued (in dollars per share)	$ 37.90	$ 43.77	$ 44.42	$ 50.71
Additional common units to purchase		1,350,000	600,000
Net proceeds received from sale of units, net of underwriter discounts	$ 298,000	$ 437,200	$ 198,200	$ 225,700
Class A [Member] | Partners' Capital
Partners Capital And Distributions [Line Items]
Common units, outstanding (in shares)						117,939,221
Class B [Member] | Partners' Capital
Partners Capital And Distributions [Line Items]
Common units, outstanding (in shares)						39,997