Comprehensive Income Changes in Accumulated Other Comprehensive Income By Component (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net current-period other comprehensive income	[1]	$ 480	$ 694	$ 634	$ 3,230
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]	(335)	3,066	(382)	629
Other comprehensive income or loss before reclassifications		409	682	456	3,119
Amounts reclassified from accumulated other comprehensive income		0	(88)	0	(88)
Net current-period other comprehensive income	[2]	409	594	456	3,031
Stockholders' Equity, Period End	[2]	74	3,660	74	3,660
Amortization of Net Retirement Plan Actuarial Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' Equity, Period Start	[2]	(5,628)	(7,792)	(5,737)	(7,893)
Other comprehensive income or loss before reclassifications	[2]	0	0	0	0
Amounts reclassified from accumulated other comprehensive income		72	102	181	203
Net current-period other comprehensive income	[2]	72	102	181	203
Stockholders' Equity, Period End	[2]	(5,556)	(7,690)	(5,556)	(7,690)
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]	(717)	(710)	(715)	(708)
Other comprehensive income or loss before reclassifications	[2]	0	0	0	0
Amounts reclassified from accumulated other comprehensive income		(1)	(2)	(3)	(4)
Net current-period other comprehensive income	[2]	(1)	(2)	(3)	(4)
Stockholders' Equity, Period End	[2]	(718)	(712)	(718)	(712)
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' Equity, Period Start	[2]	(6,680)	(5,436)	(6,834)	(7,972)
Other comprehensive income or loss before reclassifications	[2]	409	682	456	3,119
Amounts reclassified from accumulated other comprehensive income	[2]	71	12	178	111
Net current-period other comprehensive income	[2]	480	694	634	3,230
Stockholders' Equity, Period End	[2]	$ (6,200)	$ (4,742)	$ (6,200)	$ (4,742)

[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.