Other Comprehensive Income (Loss) (Details 1) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning				$ 549,405	$ 516,466
Net current-period other comprehensive income		$ 2,060	$ 5,074	3,485	17,734
Balances at Ending		576,915	554,435	576,915	554,435
Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning		(6,718)	9,692	(7,915)	(2,744)
Other comprehensive income before reclassifications		1,831	5,018	3,028	17,593
Amounts reclassified from accumulated other comprehensive (loss) income		0	(144)	0	(283)
Net current-period other comprehensive income		1,831	4,874	3,028	17,310
Balances at Ending		(4,887)	14,566	(4,887)	14,566
Employee Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning		(28,966)	(28,033)	(29,194)	(28,257)
Other comprehensive income before reclassifications		0	0	0	0
Amounts reclassified from accumulated other comprehensive (loss) income	[1]	229	200	457	424
Net current-period other comprehensive income		229	200	457	424
Balances at Ending		(28,737)	(27,833)	(28,737)	(27,833)
Accumulated Other Comprehensive (Loss) Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning		(35,684)	(18,341)	(37,109)	(31,001)
Other comprehensive income before reclassifications		1,831	5,018	3,028	17,593
Amounts reclassified from accumulated other comprehensive (loss) income		229	56	457	141
Net current-period other comprehensive income		2,060	5,074	3,485	17,734
Balances at Ending		$ (33,624)	$ (13,267)	$ (33,624)	$ (13,267)

[1] Amounts in parentheses indicated debits in income statement.