Other Comprehensive Income (Details 1) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning		$ 549,405	$ 516,466
Net current-period other comprehensive income		1,425	12,660
Balances at Ending		563,518	539,893
Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning		(7,915)	(2,744)
Other comprehensive income before reclassifications		1,197	12,575
Amounts reclassified from accumulated other comprehensive (loss) income		0	(139)
Net current-period other comprehensive income		1,197	12,436
Balances at Ending		(6,718)	9,692
Employee Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning		(29,194)	(28,257)
Other comprehensive income before reclassifications		0	0
Amounts reclassified from accumulated other comprehensive (loss) income	[1]	228	224
Net current-period other comprehensive income		228	224
Balances at Ending		(28,966)	(28,033)
Accumulated Other Comprehensive (Loss) Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning		(37,109)	(31,001)
Other comprehensive income before reclassifications		1,197	12,575
Amounts reclassified from accumulated other comprehensive (loss) income		228	85
Net current-period other comprehensive income		1,425	12,660
Balances at Ending		$ (35,684)	$ (18,341)

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