Equity-Based Compensation - Schedule of Total Equity-Based Compensation Expense (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Total equity-based compensation expense recognized	[1]	$ 5,612	$ 4,276	$ 11,519	$ 5,802

[1] Represents equity-based compensation expense recognized for equity incentive plans outstanding, including $3,058 and $7,015 related to the IPO during the three and six months ended March 31, 2019, respectively.