Accumulated Other Comprehensive Income (Loss) (Schedule of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 1,230,575	$ 893,421
Other comprehensive loss before reclassifications	(140,019)	(18,666)
Amounts reclassified from accumulated other comprehensive income	34	131
Net current-period other comprehensive (loss) income	(139,985)	(18,535)
Ending balance	1,117,490	876,853
Unrealized Loss on Securities Available for Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(24,698)	15,749
Other comprehensive loss before reclassifications	(140,019)	(18,666)
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive (loss) income	(140,019)	(18,666)
Ending balance	(164,717)	(2,917)
Postretirement Plans Asset (Liability)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(272)	(1,399)
Other comprehensive loss before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	34	131
Net current-period other comprehensive (loss) income	34	131
Ending balance	(238)	(1,268)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(24,970)	14,350
Ending balance	$ (164,955)	$ (4,185)