Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net income	$ 597,973	$ 579,150	$ 443,079
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss on securities available for sale during the period	277,926	(2,143,567)	(231,355)
Change in net unrealized gain on securities transferred to held-to-maturity	(649)	(737)	(971)
Reclassification adjustment for net (gains) losses included in net income	(66)	0	(69)
Total securities available for sale and transferred securities before tax amount	277,211	(2,144,304)	(232,395)
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss before tax amount	9,278	(5,005)	16,593
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) before tax amount	3,479	2,964	6,116
Total defined-benefit post-retirement benefit plans	12,757	(2,041)	22,709
Reclassification adjustments for (gains) losses included in net income:
Other comprehensive income (loss), before tax	289,968	(2,146,345)	(209,686)
Deferred tax expense (benefit)	60,893	(450,733)	(44,034)
Other comprehensive income (loss), net of tax	229,075	(1,695,612)	(165,652)
Comprehensive income	$ 827,048	$ (1,116,462)	$ 277,427