Net Income Per Limited Partner Unit - Schedule of Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands									3 Months Ended		9 Months Ended
	Nov. 12, 2020	Aug. 13, 2020	May 14, 2020	Feb. 13, 2020	Nov. 14, 2019	Aug. 14, 2019	May 15, 2019	Feb. 14, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Distribution Made to Limited Partner [Line Items]
Partner distributions declared	$ 37,600	$ 37,600	$ 37,600	$ 37,600		$ 34,400	$ 33,000	$ 31,600	$ 37,600	$ 35,900	$ 112,800	$ 103,100
Dividends declared per share (in dollars per share)	$ 0.3475	$ 0.3475	$ 0.3475	$ 0.3475		$ 0.3237	$ 0.3126	$ 0.3015
General Partner
Distribution Made to Limited Partner [Line Items]
Partner distributions declared	$ 1,200	$ 1,200	$ 1,200	$ 1,200		$ 400	$ 200	$ 0	1,200	700	3,600	1,300
Limited Partners Common Units
Distribution Made to Limited Partner [Line Items]
Partner distributions declared	18,200	18,200	18,200	18,200		17,000	16,400	15,800	18,200	17,600	54,600	50,900
Limited Partners Subordinated Units
Distribution Made to Limited Partner [Line Items]
Partner distributions declared	$ 18,200	$ 18,200	$ 18,200	$ 18,200		$ 17,000	$ 16,400	$ 15,800	$ 18,200	$ 17,600	$ 54,600	$ 50,900
Subsequent Event
Distribution Made to Limited Partner [Line Items]
Partner distributions declared					$ 35,900
Dividends declared per share (in dollars per share)					$ 0.3355
Subsequent Event | General Partner
Distribution Made to Limited Partner [Line Items]
Partner distributions declared					$ 700
Subsequent Event | Limited Partners Common Units
Distribution Made to Limited Partner [Line Items]
Partner distributions declared					17,600
Subsequent Event | Limited Partners Subordinated Units
Distribution Made to Limited Partner [Line Items]
Partner distributions declared					$ 17,600