Share-Based Payments - Summary of Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Shares
Outstanding at October 1, 2017 | shares	1,230
Granted | shares	3
Exercised | shares	(21)
Outstanding at December 31, 2017 | shares	1,212
Exercisable at December 31, 2017 | shares	1,051
Vested and expected to vest at December 31, 2017 | shares	1,207
Weighted-average Exercise Price
Outstanding at October 1, 2017 (in dollars per share) | $ / shares	$ 56.54
Granted (in dollars per share) | $ / shares	157.31
Exercised (in dollars per share) | $ / shares	33.10
Outstanding at December 31, 2017 (in dollars per share) | $ / shares	57.19
Exercisable at December 31, 2017 (in dollars per share) | $ / shares	53.34
Vested and expected to vest at December 31, 2016 (in dollars per share) | $ / shares	$ 57.06
Weighted-average Remaining Contractual Term
Outstanding at December 31, 2017	2 years 10 months 25 days
Exercisable at December 31, 2017	2 years 8 months 4 days
Vested and expected to vest at December 31, 2017	2 years 10 months 21 days
Aggregate Intrinsic Value
Outstanding at December 31, 2017 | $	$ 116,380
Exercisable at December 31, 2017 | $	105,003
Vested and expected to vest at December 31, 2017 | $	$ 116,081