Stockholders' Equity - RSU activity (Details)	3 Months Ended
	Dec. 31, 2020 $ / 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	234,899
Vested (in shares) | shares	(226,934)
Forfeited (in shares) | shares	(11,147)
Balance unvested at the end of the period (in shares) | shares	551,241
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	60.99
Vested (in dollars per share) | $ / shares	58.34
Forfeited (in dollars per share) | $ / shares	59.85
Balance unvested at the end of the period (in dollars per share) | $ / shares	$ 59.64
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	(11,690)
Balance unvested at the end of the period (in shares) | shares	737,056
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	50.77
Balance unvested at the end of the period (in dollars per share) | $ / shares	$ 53.88