Stockholders' Equity - RSU activity (Details)	3 Months Ended
	Dec. 31, 2019 $ / shares shares
Service-Based RSUs
Number of Shares
Balance unvested at the beginning of the period (in shares) | shares	422,094
Granted (in shares) | shares	329,918
Vested (in shares) | shares	(148,996)
Forfeited (in shares) | shares	(23,793)
Balance unvested at the end of the period (in shares) | shares	579,223
Weighted Average Grant-Date Fair Value
Balance unvested at the beginning of the period (in dollars per share) | $ / shares	$ 58.84
Granted (in dollars per share) | $ / shares	59.90
Vested (in dollars per share) | $ / shares	56.07
Forfeited (in dollars per share) | $ / shares	60.14
Balance unvested at the end of the period (in dollars per share) | $ / shares	$ 60.10
Performance-based RSUs
Number of Shares
Balance unvested at the beginning of the period (in shares) | shares	315,262
Forfeited (in shares) | shares	(174,824)
Balance unvested at the end of the period (in shares) | shares	140,438
Weighted Average Grant-Date Fair Value
Balance unvested at the beginning of the period (in dollars per share) | $ / shares	$ 55.67
Forfeited (in dollars per share) | $ / shares	47.36
Balance unvested at the end of the period (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	227,402
Granted (in shares) | shares	346,826
Forfeited (in shares) | shares	(33,874)
Balance unvested at the end of the period (in shares) | shares	540,354
Weighted Average Grant-Date Fair Value
Balance unvested at the beginning of the period (in dollars per share) | $ / shares	$ 66.77
Granted (in dollars per share) | $ / shares	52.51
Forfeited (in dollars per share) | $ / shares	59.87
Balance unvested at the end of the period (in dollars per share) | $ / shares	$ 58.05