Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ 6,426,683	$ 6,502,231
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax		55,584	(3,046)
Reclassification adjustment for net realized (gains) losses on sale of available-for-sale securities included in net income		(1,136)	0
Total other comprehensive income (loss) adjustments		54,456	(3,144)
Ending balance		6,349,708	8,007,206
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(75,997)	(48,726)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax		55,584	(3,046)
Reclassification adjustment for net realized (gains) losses on sale of available-for-sale securities included in net income		(1,136)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	[1]	0	0
Total other comprehensive income (loss) adjustments		54,448	(3,046)
Ending balance		(21,549)	(51,772)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(1,340)	(614)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax		0	0
Reclassification adjustment for net realized (gains) losses on sale of available-for-sale securities included in net income		0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	[1]	8	(98)
Total other comprehensive income (loss) adjustments		8	(98)
Ending balance		(1,332)	(712)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(77,337)	(49,340)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax		55,584	(3,046)
Reclassification adjustment for net realized (gains) losses on sale of available-for-sale securities included in net income		(1,136)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	[1]	8	(98)
Total other comprehensive income (loss) adjustments		54,456	(3,144)
Ending balance		$ (22,881)	$ (52,484)

[1] Included in Non-Interest Expense - Other in the Statements of Income.