Investment Securities (Summary Of Debt Securities Held-to Maturity - Contractual Maturities, Credit Quality and Other Information) (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 2,429
Due after one year through five years	52,963
Due after five years through ten years	309,859
Due after ten years	5,997,207
Amortized Cost	6,362,458	$ 6,198,339
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Due in one year or less	2,448
Due after one year through five years	54,861
Due after five years through ten years	306,139
Due after ten years	5,728,169
Fair Value	6,091,617	6,280,936
Held-to-maturity securities pledged	2,885,549	3,077,256
Moody's, Aaa Rating
Amortized Cost
Amortized Cost	372,898	377,374
Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	5,617,422	5,442,277
Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	226,724	227,106
Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	98,112	104,232
Moody's, A1 Rating
Amortized Cost
Amortized Cost	35,836	35,878
Moody's, A2 Rating
Amortized Cost
Amortized Cost	8,256	8,260
Moody's, A3 Rating
Amortized Cost
Amortized Cost	0	0
Moody's, Baa2 Rating
Amortized Cost
Amortized Cost	95	95
Moody's, Not Rated
Amortized Cost
Amortized Cost	3,115	3,117
Agency CMO
Amortized Cost
Amortized Cost	36,533	42,405
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	35,731	43,035
Agency CMO \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	36,533	42,405
Agency CMO \| Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, A1 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, A2 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, A3 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, Baa2 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, Not Rated
Amortized Cost
Amortized Cost	0	0
Agency MBS
Amortized Cost
Amortized Cost	2,915,114	2,901,593
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	2,794,878	2,961,249
Agency MBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	2,915,114	2,901,593
Agency MBS \| Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, A1 Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, A2 Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, A3 Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, Baa2 Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, Not Rated
Amortized Cost
Amortized Cost	0	0
Agency CMBS
Amortized Cost
Amortized Cost	2,548,347	2,378,475
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	2,394,602	2,345,833
Agency CMBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	2,548,347	2,378,475
Agency CMBS \| Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, A1 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, A2 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, A3 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, Baa2 Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, Not Rated
Amortized Cost
Amortized Cost	0	0
Municipal bonds and notes
Amortized Cost
Amortized Cost	696,601	705,918
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	704,661	757,490
Municipal bonds and notes \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	207,035	207,426
Municipal bonds and notes \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	117,428	119,804
Municipal bonds and notes \| Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	226,724	227,106
Municipal bonds and notes \| Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	98,112	104,232
Municipal bonds and notes \| Moody's, A1 Rating
Amortized Cost
Amortized Cost	35,836	35,878
Municipal bonds and notes \| Moody's, A2 Rating
Amortized Cost
Amortized Cost	8,256	8,260
Municipal bonds and notes \| Moody's, A3 Rating
Amortized Cost
Amortized Cost	0	0
Municipal bonds and notes \| Moody's, Baa2 Rating
Amortized Cost
Amortized Cost	95	95
Municipal bonds and notes \| Moody's, Not Rated
Amortized Cost
Amortized Cost	3,115	3,117
CMBS
Amortized Cost
Amortized Cost	165,863	169,948
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	161,745	173,329
CMBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	165,863	169,948
CMBS \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	0	0
CMBS \| Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	0	0
CMBS \| Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	0	0
CMBS \| Moody's, A1 Rating
Amortized Cost
Amortized Cost	0	0
CMBS \| Moody's, A2 Rating
Amortized Cost
Amortized Cost	0	0
CMBS \| Moody's, A3 Rating
Amortized Cost
Amortized Cost	0	0
CMBS \| Moody's, Baa2 Rating
Amortized Cost
Amortized Cost	0	0
CMBS \| Moody's, Not Rated
Amortized Cost
Amortized Cost	0	0
Pledged For Borrowings
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity securities pledged	1,026,796	1,243,139
Pledged For Municipal Deposits
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity securities pledged	$ 1,858,753	$ 1,834,117

Amount excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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