Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Changes in accumulated other comprehensive income (loss) by component, including amounts reclassified out of accumulated other comprehensive income (loss) and the related line item in the Statements of Operations where net income is presented
Accumulated other comprehensive income (loss), beginning of the period	$ (90,373)	$ (120,184)	$ (96,864)	$ (117,701)
Other comprehensive income (loss), net of tax	355	(521)	6,846	(3,004)
Other comprehensive income (loss), net of tax	355	(521)	6,846	(3,004)
Accumulated other comprehensive income (loss), end of the period	(90,018)	(120,705)	(90,018)	(120,705)
Investment securities:
Changes in accumulated other comprehensive income (loss) by component, including amounts reclassified out of accumulated other comprehensive income (loss) and the related line item in the Statements of Operations where net income is presented
Accumulated other comprehensive income (loss), beginning of the period	9,018	4,324	2,527	6,807
Other comprehensive income (loss) before reclassifications, net of tax (expense) benefit of $(392), $618, $(3,328) and $1,884, respectively	729	(1,147)	6,181	(3,498)
Realized investment (gains) losses, net of tax benefit (expense) of $202, $(169), $(237), and $(44), respectively	(374)	314	441	81
Impairment losses, net of tax expense of $0, $168, $121 and $222, respectively	0	312	224	413
Other comprehensive income (loss), net of tax	355	(521)	6,846	(3,004)
Accumulated other comprehensive income (loss), end of the period	9,373	3,803	9,373	3,803
Pension and other postretirement plans:
Changes in accumulated other comprehensive income (loss) by component, including amounts reclassified out of accumulated other comprehensive income (loss) and the related line item in the Statements of Operations where net income is presented
Accumulated other comprehensive income (loss), beginning of the period	(99,391)	(124,508)	(99,391)	(124,508)
Other comprehensive income (loss) before reclassifications, net of tax	0	0	0	0
Amortization of prior service costs, net of tax	0	0	0	0
Amortization of net actuarial loss, net of tax	0	0	0	0
Other comprehensive income (loss), net of tax	0	0	0	0
Accumulated other comprehensive income (loss), end of the period	$ (99,391)	$ (124,508)	$ (99,391)	$ (124,508)