Stockholders' Equity - RSU activity (Details)	6 Months Ended
	Mar. 31, 2021 $ / shares shares
Time-based RSUs
Number of Shares
Balance unvested at the beginning of the period (in shares) | shares	554,423
Granted (in shares) | shares	249,960
Vested (in shares) | shares	(230,975)
Forfeited (in shares) | shares	(116,969)
Balance unvested at the end of the period (in shares) | shares	456,439
Weighted Average Grant-Date Fair Value
Balance unvested at the beginning of the period (in dollars per share) | $ / shares	$ 58.54
Granted (in dollars per share) | $ / shares	61.09
Vested (in dollars per share) | $ / shares	58.34
Forfeited (in dollars per share) | $ / shares	59.17
Balance unvested at the end of the period (in dollars per share) | $ / shares	$ 59.88
Performance-based RSUs
Number of Shares
Balance unvested at the beginning of the period (in shares) | shares	137,770
Vested (in shares) | shares	(110,247)
Forfeited (in shares) | shares	(27,523)
Weighted Average Grant-Date Fair Value
Balance unvested at the beginning of the period (in dollars per share) | $ / shares	$ 61.40
Vested (in dollars per share) | $ / shares	61.40
Forfeited (in dollars per share) | $ / shares	$ 61.40
Performance and market-based RSUs
Number of Shares
Balance unvested at the beginning of the period (in shares) | shares	471,496
Granted (in shares) | shares	277,250
Forfeited (in shares) | shares	(20,542)
Balance unvested at the end of the period (in shares) | shares	728,204
Weighted Average Grant-Date Fair Value
Balance unvested at the beginning of the period (in dollars per share) | $ / shares	$ 51.56
Granted (in dollars per share) | $ / shares	57.71
Forfeited (in dollars per share) | $ / shares	55.09
Balance unvested at the end of the period (in dollars per share) | $ / shares	$ 53.80