Summary of Significant Accounting Policies - Issuance, dividends (Details) - $ / shares		3 Months Ended
	Aug. 07, 2018	Feb. 14, 2020	Dec. 31, 2019	Nov. 14, 2019	Sep. 30, 2019	Aug. 14, 2019	Jun. 30, 2019	May 14, 2019	Mar. 31, 2019	Feb. 14, 2019
Common Limited Partners
Net Income Per Limited Partner Unit
Quarterly cash distributions declared (in dollars per unit)			$ 0.5250		$ 0.5200		$ 0.5150		$ 0.5100
Series A Preferred Limited Partners
Net Income Per Limited Partner Unit
Public offering of common units	2,760,000
Quarterly cash distributions declared (in dollars per unit)		$ 0.609375		$ 0.609375		$ 0.609375		$ 0.609375		$ 0.609375