Shareholders' Equity - AOCI Components (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2015	Mar. 31, 2016
Repurchase of shares
Repurchase of common stock (in shares)	0	810,097
Aggregate cost of treasury shares purchase		$ 59,700
After-tax amounts:
Stockholders' Equity Attributable to Parent	$ 4,701,462		$ 4,895,846
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	$ 22,587		27,021
After-tax amounts:
Stockholders' Equity Attributable to Parent	14,482		17,201	$ 4,738
Defined benefit pension plan
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	(28,666)		(30,144)
After-tax amounts:
Stockholders' Equity Attributable to Parent	(17,638)		(18,578)	(17,952)
Accumulated other comprehensive income (loss)
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	(6,079)		(3,123)
After-tax amounts:
Stockholders' Equity Attributable to Parent	$ (3,156)		$ (1,377)	$ (13,214)