Accumulated Other Comprehensive (Loss) Income, Net of Tax (Schedule of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 8,177,135	$ 3,272,928	$ 3,438,325	$ 3,234,625
Other comprehensive (loss) before reclassifications	(206,671)	(3,948)	(460,882)	(39,471)
Amounts reclassified from accumulated other comprehensive (loss) income	1,062	1,564	2,130	3,105
Other comprehensive (loss), net of tax	(205,609)	(2,384)	(458,752)	(36,366)
Ending Balance	7,997,788	3,329,705	7,997,788	3,329,705
Available For Sale and Transferred Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(240,343)	37,071	4,536	67,424
Other comprehensive (loss) before reclassifications	(205,273)	(1,473)	(450,152)	(31,826)
Amounts reclassified from accumulated other comprehensive (loss) income	0	0	0	0
Other comprehensive (loss), net of tax	(205,273)	(1,473)	(450,152)	(31,826)
Ending Balance	(445,616)	35,598	(445,616)	35,598
Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(1,774)	15,546	6,070	19,918
Other comprehensive (loss) before reclassifications	(1,070)	(2,475)	(9,683)	(7,645)
Amounts reclassified from accumulated other comprehensive (loss) income	762	823	1,531	1,621
Other comprehensive (loss), net of tax	(308)	(1,652)	(8,152)	(6,024)
Ending Balance	(2,082)	13,894	(2,082)	13,894
Defined Benefit Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(33,606)	(44,343)	(33,186)	(45,086)
Other comprehensive (loss) before reclassifications	(328)	0	(1,047)	0
Amounts reclassified from accumulated other comprehensive (loss) income	300	741	599	1,484
Other comprehensive (loss), net of tax	(28)	741	(448)	1,484
Ending Balance	(33,634)	(43,602)	(33,634)	(43,602)
Accumulated Other Comprehensive Income (Loss), Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(275,723)	8,274	(22,580)	42,256
Other comprehensive (loss), net of tax	(205,609)	(2,384)	(458,752)	(36,366)
Ending Balance	$ (481,332)	$ 5,890	$ (481,332)	$ 5,890