Equity-Based Compensation - Schedule of Total Equity-Based Compensation Expense (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Total equity-based compensation expense recognized	[1]	$ 307	$ 14,951	$ 11,826	$ 20,753

[1] Represents equity-based compensation expense recognized for equity incentive plans outstanding, including $7,328 related to the IPO during the nine months ended June 30, 2019.