Other Comprehensive Income (Loss) - Schedule of Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Before-Tax Amount
Net unrealized gains/losses / Other comprehensive income (loss)	$ (56,977)	$ 12,011	$ (162,787)	$ (20,940)
Tax (Expense) Benefit
Net unrealized gains/losses / Other comprehensive income (loss)	13,957	(2,943)	39,868	5,132
Net of Tax
Change in net unrealized gain/loss during the period	(43,449)	8,489	(123,854)	(16,757)
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	429	579	935	949
Other comprehensive (loss) income	(43,020)	9,068	(122,919)	(15,808)
Net unrealized gain/loss
Before-Tax Amount
Change in net unrealized gain/loss during the period	(57,544)	11,244	(164,025)	(22,197)
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	0	0	0	(330)
Net unrealized gains/losses / Other comprehensive income (loss)	(57,544)	11,244	(164,025)	(22,527)
Tax (Expense) Benefit
Change in net unrealized gain/loss during the period	14,095	(2,755)	40,171	5,440
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	0	0	0	81
Net unrealized gains/losses / Other comprehensive income (loss)	14,095	(2,755)	40,171	5,521
Net of Tax
Change in net unrealized gain/loss during the period	(43,449)	8,489	(123,854)	(16,757)
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	0	0	0	(249)
Other comprehensive (loss) income	(43,449)	8,489	(123,854)	(17,006)
Amortization of net retirement plan actuarial gain/loss
Before-Tax Amount
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	514	712	1,129	1,476
Tax (Expense) Benefit
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	(125)	(175)	(276)	(362)
Net of Tax
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	389	537	853	1,114
Amortization of net retirement plan prior service cost
Before-Tax Amount
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	53	55	109	111
Tax (Expense) Benefit
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	(13)	(13)	(27)	(27)
Net of Tax
Reclassification adjustment for net realized loss on sale of available-for-sale debt securities included in net income	40	42	82	84
Employee benefit plans
Before-Tax Amount
Net unrealized gains/losses / Other comprehensive income (loss)	567	767	1,238	1,587
Tax (Expense) Benefit
Net unrealized gains/losses / Other comprehensive income (loss)	(138)	(188)	(303)	(389)
Net of Tax
Other comprehensive (loss) income	$ 429	$ 579	$ 935	$ 1,198