CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	$ (70,200)	$ 67,500	$ 61,000
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	(69,000)	70,900	71,200
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0	300	400
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax	22,400	(23,100)	(23,200)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	0	100	100
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, Tax	300	1,100	3,200
Realized gain on sale of securities, tax	2,100	0	(700)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(6,400)	(200)	(2,400)
Net Income (Loss) Attributable to Parent	899,200	506,600	499,200
Other comprehensive income (loss), net:
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	(69,000)	70,900	71,200
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0	300	400
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax	(1,200)	(3,100)	(9,800)
Amount reclassified from accumulated other comprehensive income	6,400	200	2,400
Net other comprehensive (loss) income	(76,600)	67,300	58,600
Accumulated other comprehensive income	15,700	92,300	25,000
Comprehensive income	822,600	573,900	557,800
Realized gain on sale of securities, tax	2,100	0	(700)
Unrealized holding gains (losses) on AFS
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(69,000)	70,900	71,200
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(6,400)	(200)	(2,300)
Other comprehensive income (loss), net:
Net other comprehensive (loss) income	(75,400)	70,700	68,900
Accumulated other comprehensive income	16,700	92,100	21,400
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(1,200)	(3,100)	(9,800)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	0
Other comprehensive income (loss), net:
Net other comprehensive (loss) income	(1,200)	(3,100)	(9,800)
Accumulated other comprehensive income	(700)	500	3,600
Impairment loss on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	100
Other comprehensive income (loss), net:
Net other comprehensive (loss) income	0	0	(100)
Accumulated other comprehensive income	0	0	0
Supplemental Employee Retirement Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	(300)	(400)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	0
Other comprehensive income (loss), net:
Net other comprehensive (loss) income	0	(300)	(400)
Accumulated other comprehensive income	$ (300)	$ (300)	$ 0