Comprehensive Income Changes in Accumulated Other Comprehensive Income By Componenet (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance	$ (7,972)	$ (7,166)	$ (4,373)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	697	(1,208)	(2,961)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	441	402	168
Other Comprehensive Income (Loss)	1,138	(806)	(2,793)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(6,834)	(7,972)	(7,166)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance	629	2,539	2,374
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(1,024)	(1,832)	232
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	13	(78)	(67)
Other Comprehensive Income (Loss)	(1,011)	(1,910)	165
Accumulated Other Comprehensive Income (Loss), Net of Tax	(382)	629	2,539
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance	(7,893)	(9,255)	(6,697)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	1,721	848	(2,846)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	435	514	288
Other Comprehensive Income (Loss)	2,156	1,362	(2,558)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(5,737)	(7,893)	(9,255)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance	(708)	(450)	(50)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	(224)	(347)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(7)	(34)	(53)
Other Comprehensive Income (Loss)	(7)	(258)	(400)
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (715)	$ (708)	$ (450)