Stock-Based Employee Benefit Plans - Summary of Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares
Shares
Outstanding at October 1, 2015 (in shares) | shares	2,024
Granted (in shares) | shares	36
Exercised (in shares) | shares	(521)
Forfeited (in shares) | shares	(18)
Outstanding at September 30, 2016 (in shares) | shares	1,521
Options exercisable at September 30, 2016 (in shares) | shares	985
Vested and expected to vest at September 30, 2016 (in shares) | shares	1,497
Weighted- average Exercise Price
Outstanding at October 1, 2014 (in dollars per share) | $ / shares	$ 46.94
Granted (in dollars per share) | $ / shares	94.84
Exercised (in dollars per share) | $ / shares	34.25
Forfeited (in dollars per share) | $ / shares	50.29
Outstanding at September 30, 2015 (in dollars per share) | $ / shares	52.37
Options exercisable at September 30, 2015 (in dollars per share) | $ / shares	44.92
Vested and expected to vest at September 30, 2015 (in dollars per share) | $ / shares	$ 52.04
Weighted- average Remaining Contractual Term
Outstanding at September 30, 2016	3 years 9 months 14 days
Exercisable at September 30, 2016	3 years 2 months 25 days
Vested and expected to vest at September 30, 2016	3 years 9 months 8 days
Aggregate Intrinsic Value
Outstanding at September 30, 2016 | $	$ 109,873
Exercisable at September 30, 2016 | $	78,461
Vested and expected to vest at September 30, 2016 | $	$ 108,573