Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Currently paid or payable
Federal	$ 8,960	$ 13,152
State	2,455	2,364
Current income tax expense (benefit)	11,415	15,516
Deferred tax expense
Federal	16,764	478
State	462	66
Total	17,226	544
Income tax expense	$ 28,641	$ 16,060