Capital Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended	9 Months Ended
	Jun. 01, 2021	Jan. 26, 2021	Sep. 15, 2020	Jun. 16, 2020	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020
Class Of Stock [Line Items]
Proceeds from issuance initial public offering				$ 819,700		$ (210)	$ 822,630
Underwriting commission and discounts				50,600
Estimated offering expenses payable				$ 9,200
Preferred stock, shares authorized						1,000,000		1,000,000
Preferred stock, par value per share						$ 0.001		$ 0.001
Common stock description of voting rights						The Class A common stock and Class B common stock provide identical economic rights, but holders of Class B common stock have limited voting rights, specifically that such holders have no right to vote, solely with respect to their shares of Class B common stock, with respect to the election, replacement or removal of directors.
Common stock description of conversion rights						Class A common stock and Class B common stock are not entitled to preemptive rights. Holders of Class B common stock may convert their shares of Class B common stock into shares of Class A common stock on a one-for-one basis, in whole or in part, at any time and from time to time at their option.
Conversion of Units of Limited Liability Company [Member]
Class Of Stock [Line Items]
Common stock member interests converted						108,162,741
Conversion of Membership Interests in Limited Liability Company [Member]
Class Of Stock [Line Items]
Common stock member interests converted						108,162,741
Common Class A [Member]
Class Of Stock [Line Items]
Shares issued during period					38,237,500		38,237,500
Common stock, shares authorized						1,100,000,000		1,100,000,000
Common stock par or stated value per share						$ 0.001		$ 0.001
Common Class A [Member] | Conversion of Units of Limited Liability Company [Member]
Class Of Stock [Line Items]
Common stock member interests converted						75,093,778
Common Class A [Member] | Conversion of Membership Interests in Limited Liability Company [Member]
Class Of Stock [Line Items]
Common stock member interests converted						75,093,778
Common Class A [Member] | Conversion of Profit Interests [Member]
Class Of Stock [Line Items]
Common stock member interests converted						2,703,243
Common Class B [Member]
Class Of Stock [Line Items]
Common stock, shares authorized						100,000,000		100,000,000
Common stock par or stated value per share						$ 0.001		$ 0.001
Common stock member interests converted			33,068,863
Common Class B [Member] | Conversion of Units of Limited Liability Company [Member]
Class Of Stock [Line Items]
Common stock member interests converted						33,068,963
Common Class B [Member] | Conversion of Membership Interests in Limited Liability Company [Member]
Class Of Stock [Line Items]
Common stock member interests converted						33,068,963
Class A Restricted Stock [Member] | Conversion of Profit Interests [Member]
Class Of Stock [Line Items]
Common stock member interests converted						5,532,037
IPO [Member]
Class Of Stock [Line Items]
Shares issued during period				38,237,500
Shares issued price				$ 23.00
IPO [Member] | Common Class A [Member]
Class Of Stock [Line Items]
Shares issued during period				38,237,500
Over-Allotment Option [Member]
Class Of Stock [Line Items]
Shares issued during period				4,987,500
Over-Allotment Option [Member] | Common Class A [Member]
Class Of Stock [Line Items]
Shares issued price	$ 43.50	$ 40.00	$ 33.25
Overallotment stock shares sold by shareholders during the period	2,250,000	3,000,000	3,750,000
Employee Stock [Member] | Common Class A [Member]
Class Of Stock [Line Items]
Common stock shares reserved for future issuance						3,477,413
Secondary Offering [Member] | Common Class A [Member]
Class Of Stock [Line Items]
Common stock par or stated value per share	$ 0.001	$ 0.001	$ 0.001
Stock shares sold by shareholders during the period	17,250,000	20,000,000	28,750,000
Estimated offering expenses	$ 1,100	$ 1,200