Share-Based Compensation (Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Intrinsic value, exercises in period	$ 43,564
Options
Outstanding at beginning of the period (shares)	7,430,000
Granted (shares)	611,000
Exercised (shares)	(2,185,000)
Forfeited (shares)	(7,000)
Outstanding at end of the period (shares)	5,849,000
Options exercisable (shares)	3,857,000
Options vested and expected to vest (shares)	5,774,000
Weighted Average Exercise Price/Share
Weighted average exercise price, outstanding, beginning balance (in dollars per share)	$ 10.30
Weighted average exercise price, granted (in dollars per share)	24.76
Weighted average exercise price, exercised (in dollars per share)	6.04
Weighted average exercise price, forfeited (in dollars per share)	19.20
Weighted average exercise price, outstanding, ending balance (in dollars per share)	13.39
Weighted average exercise price, exercisable (in dollars per share)	9.62
Weighted average exercise price, options vested and expected to vest (in dollars per share)	$ 13.25
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term, outstanding	6 years 4 months 24 days	5 years 10 months 24 days
Weighted average contractual term, exercisable	5 years 2 months 12 days
Weighted average remaining contractual term, options vested and expected to vest	6 years 3 months 18 days
Intrinsic value, outstanding	$ 75,542		$ 83,152
Intrinsic value, exercisable	64,333
Intrinsic value, options vested and expected to vest	$ 75,349