Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		$ (18,999)	$ (6,295)	$ 5,621	$ (12,044)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(12,377)	(11,123)	17,922
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(327)	(793)	(257)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		(12,704)	(11,916)	17,665
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(12,704)	386	7,462	(10,108)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(12,338)	(6,069)	17,922
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(752)	(1,007)	(352)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		(13,090)	(7,076)	17,570
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(6,295)	(6,681)	(1,841)	$ (1,936)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(39)	(5,054)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	425	214	95
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		$ 386	$ (4,840)	$ 95

[1] (2) See following table for details about these reclassifications.