Accumulated Other Comprehensive (Loss) Income, Net of Tax (Schedule of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 3,438,325	$ 3,234,625
Other comprehensive (loss) income, net of tax	(253,143)	(33,982)
Ending Balance	8,177,135	3,272,928
Available For Sale and Transferred Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	4,536	67,424
Other comprehensive (loss) before reclassifications	(244,879)	(30,353)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Other comprehensive (loss) income, net of tax	(244,879)	(30,353)
Ending Balance	(240,343)	37,071
Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	6,070	19,918
Other comprehensive (loss) before reclassifications	(8,613)	(5,170)
Amounts reclassified from accumulated other comprehensive income (loss)	769	798
Other comprehensive (loss) income, net of tax	(7,844)	(4,372)
Ending Balance	(1,774)	15,546
Defined Benefit Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(33,186)	(45,086)
Other comprehensive (loss) before reclassifications	(719)	0
Amounts reclassified from accumulated other comprehensive income (loss)	299	743
Other comprehensive (loss) income, net of tax	(420)	743
Ending Balance	(33,606)	(44,343)
Accumulated Other Comprehensive Income (Loss), Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(22,580)	42,256
Other comprehensive (loss) before reclassifications	(254,211)	(35,523)
Amounts reclassified from accumulated other comprehensive income (loss)	1,068	1,541
Other comprehensive (loss) income, net of tax	(253,143)	(33,982)
Ending Balance	$ (275,723)	$ 8,274