Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 347,318
Other comprehensive income (loss), net of tax	$ (502,416)	$ 25,242	(1,221,524)	$ (99,980)
Ending Balance	(874,206)		(874,206)
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			380,209	563,801
Other comprehensive income (loss) before reclassifications			(1,222,695)	(102,396)
Reclassification of amounts included in net income			0	0
Other comprehensive income (loss), net of tax			(1,222,695)	(102,396)
Ending Balance	(842,486)	461,405	(842,486)	461,405
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			1,171	2,416
Other comprehensive income (loss), net of tax			1,171	2,416
Ending Balance	(31,720)	(48,415)	(31,720)	(48,415)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			347,318	512,970
Other comprehensive income (loss) before reclassifications			(1,222,695)	(102,396)
Reclassification of amounts included in net income			1,171	2,416
Other comprehensive income (loss), net of tax			(1,221,524)	(99,980)
Ending Balance	$ (874,206)	$ 412,990	$ (874,206)	$ 412,990