Stock-Based Compensation - Equity Incentive Plan Activity (Detail) - $ / shares		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options, Total Options, Outstanding at September 30, 2016		1,522,000
Stock Options, Total Options, Granted		275,000
Stock Options, Total Options, Exercised / Vested		(639,000)
Stock Options, Total Options, Cancelled / Forfeited		(14,000)
Stock Options, Total Options, Outstanding at September 30, 2017		1,144,000	1,522,000
Stock Options, Total Options, Exercisable at September 30, 2017		654,000
Stock Options, Total Options, Vested and expected to vest	[1]	1,134,000
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2016		$ 37.72
Stock Options, Weighted Average Exercise Price, Granted		50.57
Stock Options, Weighted Average Exercise Price, Exercised / Vested		32.18
Stock Options, Weighted Average Exercise Price, Cancelled / Forfeited		48.96
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2017		43.76	$ 37.72
Stock Options, Weighted Average Exercise Price, Exercisable at September 30, 2017		41.58
Stock Options, Weighted Average Exercise Price, Vested and expected to vest	[1]	43.74
Stock Options, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2016		12.53
Stock Options, Weighted Average Grant Date Fair Value, Granted		12.76
Stock Options, Weighted Average Grant Date Fair Value, Exercised / Vested		11.05
Stock Options, Weighted Average Grant Date Fair Value, Cancelled / Forfeited		13.41
Stock Options, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2017		$ 13.40	$ 12.53
Restricted Stock / Units, Outstanding at September 30, 2017		12,047
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock / Units, Outstanding at September 30, 2016	[2]	732,000
Restricted Stock / Units, Granted	[2]	303,000
Restricted Stock / Units, Performance-based adjustment	[2],[3]	10,000
Restricted Stock / Units, Exercised / Vested	[2]	(147,000)
Restricted Stock / Units, Cancelled / Forfeited	[2]	(22,000)
Restricted Stock / Units, Outstanding at September 30, 2017	[2]	876,000	732,000
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2016		$ 43.54
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Granted		51.03	$ 40.51	$ 45.85
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Performance-based adjustment	[3]	46.02
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Exercised / Vested		47.60
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Cancelled / Forfeited		45.52
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2017		$ 45.43	$ 43.54

[1] Stock options vested and expected to vest in the future, net of estimated forfeitures, have a weighted average remaining contractual life of 6.05 years.

[2] The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.

[3] Represents the net incremental number of shares issuable upon vesting of performance-based restricted stock units based upon the achievement of the annual financial performance metrics for fiscal 2017.