Comprehensive Income (Loss) (Schedule of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 764,230	$ 692,979
Other comprehensive income (loss) before reclassifications	13,510	(7,128)
Amounts reclassified from accumulated other comprehensive income	339	79
Net current-period other comprehensive income (loss)	13,849	(7,049)
Ending balance	815,169	724,722
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	13,510	(7,128)
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive income (loss)	13,510	(7,128)
Ending balance	4,016	(8,822)
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	339	79
Net current-period other comprehensive income (loss)	339	79
Ending balance	(2,128)	(2,373)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(11,961)	(4,146)
Ending balance	$ 1,888	$ (11,195)