Current and Deferred Income Tax (Benefit) and Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred Income Tax Assets And Liabilities
Income before income taxes	$ 28,670	$ 31,138
Current tax expense	1,228	8,922
Deferred tax expense	8,712	3,941
Deferred tax benefit - impact of tax reform	(11,452)
Total deferred tax (benefit) expense	(2,740)	3,941
Total tax (benefit) expense	$ (1,512)	$ 12,863