Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income	$ 443,079	$ 331,151	$ 443,599
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss on securities available for sale during the period	(231,355)	427,331	418,556
Change in net unrealized gain on securities transferred to held-to-maturity	(971)	(1,256)	(1,292)
Reclassification adjustment for net (gains) losses included in net income	(69)	(108,989)	(293)
Total securities available for sale and transferred securities before tax amount	(232,395)	317,086	416,971
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss before tax amount	16,593	(11,518)	(3,644)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) before tax amount	6,116	5,319	5,623
Total defined-benefit post-retirement benefit plans	22,709	(6,199)	1,979
Reclassification adjustments for (gains) losses included in net income:
Other comprehensive income (loss), before tax	(209,686)	310,887	418,950
Deferred tax expense (benefit)	(44,034)	65,287	87,980
Other comprehensive income (loss), net of tax	(165,652)	245,600	330,970
Comprehensive income	$ 277,427	$ 576,751	$ 774,569