Share-Based Payments - Summary of Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Shares
Outstanding at September 30, 2019 (in shares) | shares	616
Granted (in shares) | shares	16
Exercised (in shares) | shares	(93)
Forfeited (in shares) | shares	(1)
Outstanding at December 31, 2019 (in shares) | shares	538
Exercisable at December 31, 2019 (in shares) | shares	458
Vested and expected to vest at December 31, 2019 (in shares) | shares	533
Weighted-average Exercise Price
Outstanding at October 1, 2017 (in dollars per share) | $ / shares	$ 89.36
Granted (in dollars per share) | $ / shares	352.18
Exercised (in dollars per share) | $ / shares	54.51
Forfeited (in dollars per share) | $ / shares	185.05
Outstanding at December 31, 2017 (in dollars per share) | $ / shares	103.12
Exercisable at December 31, 2017 (in dollars per share) | $ / shares	81.93
Vested and expected to vest at December 31, 2016 (in dollars per share) | $ / shares	$ 101.77
Weighted-average Remaining Contractual Term
Outstanding at December 31, 2019	2 years 11 months 8 days
Exercisable at December 31, 2019	2 years 4 months 20 days
Vested and expected to vest at December 31, 2019	2 years 10 months 28 days
Aggregate Intrinsic Value
Outstanding at December 31, 2019 | $	$ 146,033
Exercisable at December 31, 2019 | $	134,066
Vested and expected to vest at December 31, 2019 | $	$ 145,490