Accumulated Other Comprehensive Income (Changes in AOCI by Component) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 182,195	$ 40,367
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(102,605)	97,673
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(1,862)	(833)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total	(104,467)	96,840
Ending balance	77,728	137,207
Unrealized Gains and Losses on Available-for-Sale Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	163,174	33,038
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(102,605)	79,696
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	0	(191)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total	(102,605)	79,505
Ending balance	60,569	112,543
Unrealized Gains and Losses on Pension Plan Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(5,833)	(3,974)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	115	80
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total	115	80
Ending balance	(5,718)	(3,894)
Unrealized gains and losses on cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	24,854	11,303
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	17,977
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(1,977)	(722)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total	(1,977)	17,255
Ending balance	$ 22,877	$ 28,558