SHAREHOLDERS’ EQUITY - AOCI Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Repurchase of shares
Repurchase of common stock (in shares)	0	0	810,097
Aggregate cost of treasury shares purchase			$ 59,654
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	$ 2,300	$ (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	$ 31,700	33,051	27,021
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	20,070	20,899	17,201
Defined benefit pension plan
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	(28,873)	(34,112)	(30,144)
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	(17,770)	(21,103)	(18,578)
Accumulated Other Comprehensive Loss
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	2,827	(1,061)	(3,123)
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	$ 2,300	$ (204)	$ (1,377)