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Earnings Per Share - Antidilutive Securities (Details) - $ / shares	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Feb. 18, 2020	Feb. 13, 2020
Class A Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Exchangeable notes, exchange price per share (in USD per share)					$ 40.87
Warrants sold in connection with the issuance of the Exchangeable notes (in USD per share)						$ 62.88
Restricted Class A Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	2,949	193,709	8,965	225,985
Out-of-the-money Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	2,100,833	1,498,000	2,419,305	1,105,000
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	1,678,774	1,127,509	1,531,722
Class B Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	10,229,142	12,404,368	10,884,874	12,699,339