CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net income		$ 302,864	$ 305,072	$ 281,025
Available-for-sale debt securities:
Net unrealized holding gains (losses) on debt securities	[1]	165,420	(718,582)	(143,115)
Defined benefit plans adjustments:
Net actuarial gain (loss)		177	(2,199)	3,660
Reclassification adjustment for amortization of net actuarial loss		11	2	1
Other comprehensive income (loss) for the year, net of tax		165,608	(720,779)	(139,454)
Total comprehensive income (loss)		468,472	(415,707)	141,571
Income tax effect of items included in other comprehensive income (loss):
Net actuarial gain (loss)		(107)	1,319	(2,199)
Reclassification adjustment for amortization of net actuarial loss		(6)	(1)	0
Total income tax effect of items included in other comprehensive income (loss)		$ (113)	$ 1,318	$ (2,199)

[1] (1) Net unrealized gains (losses) on available-for-sale   debt securities have no tax effect because securities   are either tax-exempt, held by an International   Banking Entity ("IBE") unit or subsidiary, or have a full deferred tax asset valuation allowance.