Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Current:
Federal	$ 7,578	$ 18,724	$ 28,793
State	2,664	5,344	8,143
Deferred
Federal	8,775	7,485	(3,719)
State	1,359	2,185	(382)
Income tax expense	$ 20,376	$ 33,738	$ 32,835