Accumulated Other Comprehensive Income (Loss) (Schedule of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 764,230	$ 692,979	$ 368,101
Other comprehensive income (loss) before reclassifications	16,545	(7,831)	1,413
Amounts reclassified from accumulated other comprehensive income	539	16	284
Net current-period other comprehensive income (loss)	17,084	(7,815)	1,697
Ending balance	852,401	764,230	692,979
Unrealized Gain (Loss) on Securities Available for Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(9,494)	(1,694)	(1,947)
Other comprehensive income (loss) before reclassifications	17,073	(7,800)	405
Amounts reclassified from accumulated other comprehensive income	(75)	0	148
Net current-period other comprehensive income (loss)	16,998	(7,800)	553
Reclassification of accumulated other comprehensive income to retained earnings due to statutory tax changes			(300)
Ending balance	7,504	(9,494)	(1,694)
Postretirement Plans Asset (Liability)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,467)	(2,452)	(3,160)
Other comprehensive income (loss) before reclassifications	(528)	(31)	1,008
Amounts reclassified from accumulated other comprehensive income	614	16	136
Net current-period other comprehensive income (loss)	86	(15)	1,144
Reclassification of accumulated other comprehensive income to retained earnings due to statutory tax changes			(436)
Ending balance	(2,381)	(2,467)	(2,452)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(11,961)	(4,146)	(5,107)
Reclassification of accumulated other comprehensive income to retained earnings due to statutory tax changes			(736)
Ending balance	$ 5,123	$ (11,961)	$ (4,146)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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