Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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 year	$ (117,701)	$ (59,099)	$ (133,191)
Other comprehensive (loss) income, net of tax	(4,280)	823	(7,341)
Other comprehensive income (loss), net of tax	(25,117)	59,425	(81,433)
Other comprehensive income, net of tax	20,837	(58,602)	74,092
Accumulated other comprehensive income (loss), end of the year	(96,864)	(117,701)	(59,099)
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 year	6,807	5,984	13,325
Other comprehensive (loss) income before reclassifications, net of tax benefit (expense) of $2,678, $(633), and $3,852, respectively	(4,973)	1,175	(7,153)
Realized investment gains, net of tax benefit of $172, $226 and $236, respectively	320	420	440
Impairment losses, net of tax expense of $(545), $(37), and $(136), respectively	(1,013)	(68)	(252)
Other comprehensive (loss) income, net of tax	(4,280)	823	(7,341)
Accumulated other comprehensive income (loss), end of the year	2,527	6,807	5,984
Investment securities, tax
Other comprehensive (loss) income, unrealized holding (loss) gain on investment securities, tax benefit (expense)	2,678	(633)	3,852
Reclassification adjustment for realized investment gains, tax benefit	172	226	236
Reclassification adjustment for impairment losses, tax expense	(545)	(37)	(136)
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 year	(124,508)	(65,083)	(146,516)
Other comprehensive income (loss) before reclassifications, net of tax (expense) benefit of $(8,433), $34,378, and $(38,352), respectively	15,661	(63,845)	71,226
Amortization of prior service costs, net of tax expense of $234, $248, and $278, respectively	434	461	517
Amortization of net actuarial loss, net of tax expense of $4,858, $2,131, and $5,218, respectively	9,022	3,959	9,690
Other comprehensive income (loss), net of tax	25,117	(59,425)	81,433
Accumulated other comprehensive income (loss), end of the year	(99,391)	(124,508)	(65,083)
Pension and other postretirement plans, tax
Other comprehensive income (loss), pension and other postretirement plans, tax (expense) benefit	(8,433)	34,378	(38,352)
Reclassification adjustment for amortization of prior service costs, tax expense	234	248	278
Reclassification adjustment for amortization of net actuarial loss, tax expense	$ 4,858	$ 2,131	$ 5,218