Shareholders' Equity - AOCI Components (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 31, 2017	Sep. 30, 2016
Repurchase of shares
Repurchase of common stock (in shares)	0	0
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	$ 2,433	$ (204)
Maximum
Repurchase of shares
Number of common shares authorized to be repurchased	4,000,000
Unrealized appreciation (depreciation) on securities
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	$ 36,158	33,051
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	22,804	20,899
Defined benefit pension plan
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	(32,962)	(34,112)
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	(20,371)	(21,103)
Accumulated Other Comprehensive Income (Loss)
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	3,196	(1,061)
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	$ 2,433	$ (204)