Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Unrealized holding gains (losses) on available-for-sale securities during the period, pre-tax		$ (21,309)		$ (105,497)		$ 21,591	$ (217,894)
Reclassification adjustment for gains (losses) included in net income, pre-tax	[1]	0		31		(120)	31
Net unrealized holding (losses) gains		(21,309)		(105,466)		21,471	(217,863)
Change in funded status of post-retirement health plan, pre-tax				(2)			(3)
Net other comprehensive income (loss), pre-tax		(21,309)		(105,468)		21,471	(217,866)
Unrealized holding gains (losses) on available-for-sale securities during the period, tax		4,475		22,154		(4,534)	45,758
Reclassification adjustment for gains (losses) included in net income, tax	[1]	0		(6)		25	(7)
Net unrealized gains on available-for-sale securities, tax		4,475		22,148		(4,509)	45,751
Change in funded status of post-retirement health plan, tax				0			0
Net other comprehensive income (loss), tax		4,475		22,148		(4,509)	45,751
Unrealized holding gains (losses) on available-for-sale securities during the period, after-tax		(16,834)		(83,343)		17,057	(172,136)
Reclassification adjustment for gains (losses) included in net income, after-tax	[1]	0		25		(95)	24
Unrealized holding (losses) gains, net of reclassification and tax		(16,834)		(83,318)		16,962	(172,112)
Change in funded status of post-retirement plan, net of tax		0		(2)		0	(3)
Other comprehensive (loss) income, net of tax		$ (16,834)	$ 33,796	$ (83,320)	$ (88,795)	$ 16,962	$ (172,115)

[1] Pre-tax reclassification adjustments relating to available-for-sale securities are reported in security gains and the tax impact is included in income tax expense on the consolidated statements of income.