Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator for diluted and basic earnings per share:
Net income	$ 20,548	$ 19,622	$ 58,276	$ 61,538
Denominator - share:
Basic weighted-average shares	34,210	35,499	34,458	35,400
Effect of dilutive securities	952	886	962	940
Diluted weighted-average shares	35,162	36,385	35,420	36,340
Earnings per share:
Basic	$ 0.60	$ 0.55	$ 1.69	$ 1.74
Diluted	$ 0.58	$ 0.54	$ 1.65	$ 1.69