Related Person Transactions - Footnotes to Revenue from Related Parties (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
DHC
Related Party Transaction [Line Items]
Aggregate incentive business management fees	$ 40,642	$ 55,740
SIR
Related Party Transaction [Line Items]
Aggregate incentive business management fees	25,817	25,569
SVC
Related Party Transaction [Line Items]
Aggregate incentive business management fees	$ 53,635	$ 74,572