CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net income	$ 281,025	$ 102,273	$ 167,377
Debt securities:
Unrealized gain on debt securities for which credit losses has been recognized	1,417	772	48
Reclassification adjustment for credit loss - (benefit) expense on debt securities included in net income	(136)	1,641	497
Reclassification adjustment for net gains included in net income on sales of available-for-sale securities with no credit losses previously recognized	0	(13,198)	0
All other unrealized holding (losses) gains on available-for-sale securities	(144,396)	59,746	46,634
Defined benefit plans adjustments:
Net actuarial gain (loss)	3,661	(270)	0
Other comprehensive (loss) income for the year, net of tax	(139,454)	48,691	47,179
Total comprehensive income	141,571	150,964	214,556
Income tax effect of items included in other comprehensive (loss) income:
Unrealized gain on debt securities for which credit losses have been recognized, tax	0	0	0
Reclassification adjustment for credit losses - (benefit) expense on debt securities included in net income, tax	0	0	0
Reclassification adjustments for net gain included in net income on sales of available-for-sale debt securities with no credit losses previously recognized, tax	0	0	0
All other unrealized holding (losses) gains on available-for-sale debt securities, tax	0	0	0
Net actuarial gain (loss), tax	2,199	(162)	0
Total income tax effect of items included in other comprehensive (loss) income	$ 2,199	$ (162)	$ 0