Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 347,318
Other comprehensive income (loss), net of tax	$ (654,719)	$ (62,707)	(1,876,243)	$ (162,687)
Ending Balance	(1,528,925)		(1,528,925)
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			380,209	563,801
Other comprehensive income (loss) before reclassifications			(1,877,999)	(166,311)
Reclassification of amounts included in net income			0	0
Other comprehensive income (loss), net of tax			(1,877,999)	(166,311)
Ending Balance	(1,497,790)	397,490	(1,497,790)	397,490
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(32,891)	(50,831)
Other comprehensive income (loss) before reclassifications			0	0
Reclassification of amounts included in net income			1,756	3,624
Other comprehensive income (loss), net of tax			1,756	3,624
Ending Balance	(31,135)	(47,207)	(31,135)	(47,207)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			347,318	512,970
Other comprehensive income (loss) before reclassifications			(1,877,999)	(166,311)
Reclassification of amounts included in net income			1,756	3,624
Other comprehensive income (loss), net of tax			(1,876,243)	(162,687)
Ending Balance	$ (1,528,925)	$ 350,283	$ (1,528,925)	$ 350,283