Equity-Based Compensation - Schedule of Weighted-Average Assumptions Used in Valuation of Unit Awards, Restricted Stock Unit Awards Were Converted and Stock Option Awards Granted or Modified (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2019	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	1.37%	2.85%	2.77%
Volatility factor	46.00%	38.85%	26.93%
Expected term (in years)	2 years 7 months 6 days	6 years 3 months 18 days	6 years