Equity-Based Compensation - Schedule of Total Equity-Based Compensation Expense (Details) - USD ($) $ in Thousands		3 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Total equity-based compensation expense recognized	[1]	$ 5,908	$ 1,526

[1] Represents equity-based compensation expense recognized for equity incentive plans outstanding, including $3,957 related to the IPO during the three months ended December 31, 2018.