Comprehensive Income Changes in Accumulated Other Comprehensive Income By Component (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017		Mar. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net current-period other comprehensive income	[1]	$ 154		$ 2,536
Unrealized Gains and Losses on Available for Sale Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' Equity, Period Start	[2]	(382)		629
Other comprehensive income or loss before reclassifications		47		2,437
Amounts reclassified from accumulated other comprehensive income		0	[1]	0	[2]
Net current-period other comprehensive income	[2]	47		2,437
Stockholders' Equity, Period End	[2]	(335)		3,066
Amortization of Net Retirement Plan Actuarial Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' Equity, Period Start	[2]	(5,737)		(7,893)
Other comprehensive income or loss before reclassifications	[2]	0		0
Amounts reclassified from accumulated other comprehensive income		109		101
Net current-period other comprehensive income	[2]	109		101
Stockholders' Equity, Period End	[2]	(5,628)		(7,792)
Accretion of Net Retirement Plan Prior Service Credit
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' Equity, Period Start	[2]	(715)		(708)
Other comprehensive income or loss before reclassifications	[2]	0		0
Amounts reclassified from accumulated other comprehensive income		(2)		(2)
Net current-period other comprehensive income	[2]	(2)		(2)
Stockholders' Equity, Period End	[2]	(717)		(710)
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' Equity, Period Start	[2]	(6,834)		(7,972)
Other comprehensive income or loss before reclassifications	[2]	47		2,437
Amounts reclassified from accumulated other comprehensive income	[2]	107		99
Net current-period other comprehensive income	[2]	154		2,536
Stockholders' Equity, Period End	[2]	$ (6,680)		$ (5,436)

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost.

[2] All amounts are net of tax. Amounts in parentheses indicate debits.