Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net Income (Loss)	$ 159,032	$ 192,113	$ 242,260
Debt securities available-for-sale:
Net change in unrealized gains (losses) on debt securities available-for-sale	38,535	(339,422)	(67,652)
Related income tax (expense) benefit	(10,045)	82,253	16,112
Net securities losses (gains) reclassified into earnings	241	13	(56)
Related income tax (benefit) expense	(58)	(3)	13
Net effect on other comprehensive income for the period	28,673	(257,159)	(51,583)
Defined benefit plans:
Amortization of net loss and prior service costs	399	291	2,521
Related income tax benefit	(97)	(70)	(609)
Recognition of unrealized gain (loss)	8,909	(473)	17,386
Related income tax (expense) benefit	(2,161)	115	(4,194)
Net effect on other comprehensive income for the period	7,050	(137)	15,104
Total other comprehensive gain (loss)	35,723	(257,296)	(36,479)
Comprehensive income (loss)	$ 194,755	$ (65,183)	$ 205,781