Stock-Based Employee Benefit Plans - Summary of Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Shares
Outstanding at October 1, 2014 | shares	2,089
Granted | shares	552
Exercised | shares	(545)
Forfeited | shares	(72)
Outstanding at September 30, 2015 | shares	2,024
Options exercisable at September 30, 2015 | shares	1,005
Vested and expected to vest at September 30, 2015 | shares	1,918
Weighted- average Exercise Price
Outstanding at October 1, 2014 (in dollars per share)	$ 36.24
Granted (in dollars per share)	73.37
Exercised (in dollars per share)	33.46
Forfeited (in dollars per share)	41.47
Outstanding at September 30, 2015 (in dollars per share)	46.94
Options exercisable at September 30, 2015 (in dollars per share)	35.51
Vested and expected to vest at September 30, 2015 (in dollars per share)	$ 46.06
Weighted- average Remaining Contractual Term
Outstanding at September 30, 2015	4 years 3 months 22 days
Options exercisable at September 30, 2015	3 years 5 months 9 days
Vested and expected to vest at September 30, 2015	4 years 3 months 4 days
Aggregate Intrinsic Value
Outstanding at September 30, 2015 | $	$ 76,075
Options exercisable at September 30, 2015 | $	49,230
Vested and expected to vest at September 30, 2015 | $	$ 73,769