Partners' Equity, Cash Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Allocations of Quarterly Cash Distributions to General and Limited Partners
Partners' Capital, Distribution Amount Per Share	$ 0.555		$ 0.555
Partner Distributions
General partner interest	$ 901	$ 825	$ 2,639	$ 2,422
Incentive Distribution, Distribution	10,347	8,517	29,491	24,283
Total general partner distribution	11,248	9,342	32,130	26,705
Limited partner distribution	32,554	30,648	96,051	90,625
Total regular quarterly cash distribution	$ 43,802	$ 39,990	$ 128,181	$ 117,330
Cash distribution per unit applicable to limited partners	$ 0.5550	$ 0.5225	$ 1.6375	$ 1.5450
Subsequent Event [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared	Oct. 22, 2015
Dividends Payable, Date to be Paid	Nov. 13, 2015
Dividends Payable, Date of Record	Nov. 02, 2015