Partnership Distributions - Summary of Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Oct. 26, 2017	Sep. 30, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Distribution Made to Limited Partner [Line Items]
Distribution ($ per unit)			$ 0.4883	$ 0.4665	$ 0.4457	$ 0.4108	$ 0.4333
Distributions			$ 19,851	$ 16,971	$ 16,089	$ 13,066	$ 13,782
Incentive distribution			520	223	92	0	$ 0
Common Units
Distribution Made to Limited Partner [Line Items]
Distribution ($ per unit)	$ 0.5110	$ 0.0408					$ 0.3925
Distributions			11,566	9,330	8,909	6,533	$ 6,891
Subordinated Unitholders
Distribution Made to Limited Partner [Line Items]
Distributions			$ 7,765	$ 7,418	$ 7,088	$ 6,533	$ 6,891