Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Current:
Federal	$ 28,793	$ 19,747	$ 14,486
State	8,143	4,909	3,759
Deferred	(4,101)	659	1,676
Income tax expense	$ 32,835	$ 25,315	$ 19,921