Schedule of Other Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Assets [Abstract]
Goodwill, net	$ 311,897	$ 314,143	$ 331,884
Investments	48,142	41,287
Prepaid and other	24,605	17,937
Derivative assets	2,642	17,482
Furniture, fixtures, and equipment, net	6,431	6,127
Deferred financing costs, net	5,228	6,851
Total other assets	$ 398,945	$ 403,827