Other Comprehensive Income (Loss) - Tax Effect Allocated to Each Component of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Before-Tax Amount
Change in net unrealized gain (loss) during the period		$ 4,516
Net unrealized gains/losses / Other comprehensive (loss) income	$ 7,578	110,841	$ (202,310)
Tax (Expense) Benefit
Reclassification adjustment		(1,106)
Other Comprehensive Income, Net unrealized losses	(1,065)	(27,157)	49,571
Net of Tax
Other comprehensive gain (loss), before reclassifications		3,410
Other comprehensive income (loss)	6,513	83,684	(152,739)
Available-for-sale securities
Before-Tax Amount
Change in net unrealized gain (loss) during the period	(3,709)	35,008	(229,463)
Reclassification adjustment for net realized gains on sale of available-for-sale debt securities included in net income	(50)	69,984	11,916
Net unrealized gains/losses / Other comprehensive (loss) income	(3,759)	104,992	(217,547)
Tax (Expense) Benefit
Other comprehensive gain (loss), before reclassifications	1,588	(8,578)	56,223
Reclassification adjustment	12	(17,146)	(2,919)
Other Comprehensive Income, Net unrealized losses	1,600	(25,724)	53,304
Net of Tax
Other comprehensive gain (loss), before reclassifications	(2,121)	26,430	(173,240)
Reclassification adjustment	(38)	52,838	8,997
Other comprehensive income (loss)	(2,159)	79,268	(164,243)
Net retirement plan actuarial (loss) gain
Before-Tax Amount
Change in net unrealized gain (loss) during the period	10,240		12,761
Reclassification adjustment for net realized gains on sale of available-for-sale debt securities included in net income	915	1,116	2,260
Tax (Expense) Benefit
Other comprehensive gain (loss), before reclassifications	(2,408)		(3,127)
Reclassification adjustment	(215)	(273)	(554)
Net of Tax
Other comprehensive gain (loss), before reclassifications	7,832		9,634
Reclassification adjustment	700	843	1,706
Amortization of net retirement plan prior service cost
Before-Tax Amount
Reclassification adjustment for net realized gains on sale of available-for-sale debt securities included in net income	182	217	216
Tax (Expense) Benefit
Reclassification adjustment	(42)	(54)	(52)
Net of Tax
Reclassification adjustment	140	163	164
Employee benefit plans
Before-Tax Amount
Net unrealized gains/losses / Other comprehensive (loss) income	11,337	5,849	15,237
Tax (Expense) Benefit
Other Comprehensive Income, Net unrealized losses	(2,665)	(1,433)	(3,733)
Net of Tax
Other comprehensive income (loss)	$ 8,672	$ 4,416	$ 11,504