Stock-Based Compensation - Equity Incentive Plan Activity (Detail) - $ / shares		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options, Total Options, Outstanding at September 30, 2015		1,510,000
Stock Options, Total Options, Granted		385,000
Stock Options, Total Options, Exercised / Vested		(339,000)
Stock Options, Total Options, Cancelled / Forfeited		(34,000)
Stock Options, Total Options, Outstanding at September 30, 2016		1,522,000	1,510,000
Stock Options, Total Options, Exercisable at September 30, 2016		1,134,000
Stock Options, Total Options, Vested and expected to vest	[1]	1,515,000
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2015		$ 33.91
Stock Options, Weighted Average Exercise Price, Granted		40.35
Stock Options, Weighted Average Exercise Price, Exercised / Vested		23.03
Stock Options, Weighted Average Exercise Price, Cancelled / Forfeited		42.33
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2016		37.72	$ 33.91
Stock Options, Weighted Average Exercise Price, Exercisable at September 30, 2016		35.93
Stock Options, Weighted Average Exercise Price, Vested and expected to vest	[1]	37.69
Stock Options, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2015		11.65
Stock Options, Weighted Average Grant Date Fair Value, Granted		11.12
Stock Options, Weighted Average Grant Date Fair Value, Exercised / Vested		6.80
Stock Options, Weighted Average Grant Date Fair Value, Cancelled / Forfeited		13.49
Stock Options, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2016		$ 12.53	$ 11.65
Restricted Stock / Units, Outstanding at September 30, 2016		22,305
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock / Units, Outstanding at September 30, 2015	[2]	735,000
Restricted Stock / Units, Granted	[2]	442,000
Restricted Stock / Units, Performance-based adjustment	[2],[3]	(27,000)
Restricted Stock / Units, Exercised / Vested	[2]	(335,000)
Restricted Stock / Units, Cancelled / Forfeited	[2]	(83,000)
Restricted Stock / Units, Outstanding at September 30, 2016	[2]	732,000	735,000
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2015		$ 43.84
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Granted		40.51	$ 45.85	$ 47.63
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Performance-based adjustment	[3]	45.44
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Exercised / Vested		39.28
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Cancelled / Forfeited		45.10
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2016		$ 43.54	$ 43.84

[1] Stock options vested and expected to vest in the future, net of estimated forfeitures, have a weighted average remaining contractual life of 5.18 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 number of performance based restricted stock units cancelled based on the Company’s actual performance against performance targets applicable to outstanding restricted stock units.