Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands							6 Months Ended	12 Months Ended
	May 15, 2019	Feb. 14, 2019	Nov. 14, 2018	Aug. 14, 2018	May 15, 2018	Feb. 14, 2018	Jun. 30, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Cash distribution per unit (in dollars per share)		$ 0.9975	$ 0.9775	$ 0.9575	$ 0.9375	$ 0.9200		$ 3.7925
Total cash distributions		$ 227,832	$ 223,061	$ 218,497	$ 213,933	$ 209,940		$ 865,431
Scenario, Forecast
Subsequent Event [Line Items]
Cash distribution per unit (in dollars per share)	$ 1.0050						$ 2.0025
Total cash distributions	$ 229,545						$ 457,377