Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013
After-tax amounts:
Accumulated other comprehensive income, after-tax	$ 113,425	$ 129,716	$ 132,530
Unrealized appreciation on securities
Pre-tax amounts:
Accumulated other comprehensive income, pre-tax	205,068		237,214
After-tax amounts:
Accumulated other comprehensive income, after-tax	124,764	141,200	144,161
Unrecognized actuarial loss
Pre-tax amounts:
Accumulated other comprehensive income, pre-tax	(18,752)		(19,210)
After-tax amounts:
Accumulated other comprehensive income, after-tax	(11,339)		(11,631)
Total
Pre-tax amounts:
Accumulated other comprehensive income, pre-tax	186,316		218,004
After-tax amounts:
Accumulated other comprehensive income, after-tax	$ 113,425		$ 132,530