Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Numerator for diluted and basic earnings per share:
Net income	$ 19,241	$ 14,407
Denominator - share:
Basic weighted-average shares	31,185	31,936
Effect of dilutive securities	1,251	1,192
Diluted weighted-average shares	32,436	33,128
Earnings per share:
Basic (in dollars per share)	$ 0.62	$ 0.45
Diluted (in dollars per share)	$ 0.59	$ 0.43