Comprehensive Income (Loss) (Schedule of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 764,230	$ 692,979
Other comprehensive income (loss) before reclassifications	15,212	(7,839)
Amounts reclassified from accumulated other comprehensive income	383	12
Net current-period other comprehensive income (loss)	15,595	(7,827)
Ending balance	834,982	743,076
Unrealized Gain (Loss) on Securities Available for Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(9,494)	(1,694)
Other comprehensive income (loss) before reclassifications	15,212	(7,839)
Amounts reclassified from accumulated other comprehensive income	(75)	0
Net current-period other comprehensive income (loss)	15,137	(7,839)
Ending balance	5,643	(9,533)
Additional Pension Asset (Liability)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,467)	(2,452)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	458	12
Net current-period other comprehensive income (loss)	458	12
Ending balance	(2,009)	(2,440)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(11,961)	(4,146)
Ending balance	$ 3,634	$ (11,973)