Investment Securities (Summary Of Debt Securities Held-to Maturity - Contractual Maturities, Credit Quality and Other Information) (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Amortized Cost
Maturing within 1 year	$ 4,341
After 1 year through 5 years	55,954
After 5 through 10 years	344,666
After 10 years	6,539,039
Amortized Cost	6,944,000	$ 6,564,879
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Maturing within 1 year	4,340
After 1 year through 5 years	56,141
After 5 through 10 years	326,276
After 10 years	5,679,925
Fair Value	6,066,682	5,761,453
Held-to-maturity securities pledged	6,340,235	1,857,512
Moody's, Aaa Rating
Amortized Cost
Amortized Cost	438,998	485,648
Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	6,083,346	5,649,733
Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	254,457	255,235
Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	116,030	116,870
Moody's, A1 Rating
Amortized Cost
Amortized Cost	32,949	38,177
Moody's, A2 Rating
Amortized Cost
Amortized Cost	0	4,165
Moody's, A3 Rating
Amortized Cost
Amortized Cost	4,165	0
Moody's, Not Rated
Amortized Cost
Amortized Cost	14,055	15,051
Pledged For Municipal Deposits
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity securities pledged	1,259,307	1,596,777
Pledged For Borrowings
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity securities pledged	5,080,928	260,735
Agency CMO
Amortized Cost
Amortized Cost	25,791	28,358
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	23,658	26,298
Agency CMO \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	25,791	28,358
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, Not Rated
Amortized Cost
Amortized Cost	0	0
Agency MBS
Amortized Cost
Amortized Cost	2,541,384	2,626,114
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	2,216,476	2,287,349
Agency MBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	2,541,384	2,626,114
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, Not Rated
Amortized Cost
Amortized Cost	0	0
Agency CMBS
Amortized Cost
Amortized Cost	3,353,205	2,831,949
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	2,847,695	2,425,146
Agency CMBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	3,353,205	2,831,949
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, Not Rated
Amortized Cost
Amortized Cost	0	0
Municipal bonds and notes
Amortized Cost
Amortized Cost	919,112	928,845
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	883,647	882,760
Municipal bonds and notes \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	334,490	336,035
Municipal bonds and notes \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	162,966	163,312
Municipal bonds and notes \| Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	254,457	255,235
Municipal bonds and notes \| Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	116,030	116,870
Municipal bonds and notes \| Moody's, A1 Rating
Amortized Cost
Amortized Cost	32,949	38,177
Municipal bonds and notes \| Moody's, A2 Rating
Amortized Cost
Amortized Cost	0	4,165
Municipal bonds and notes \| Moody's, A3 Rating
Amortized Cost
Amortized Cost	4,165	0
Municipal bonds and notes \| Moody's, Not Rated
Amortized Cost
Amortized Cost	14,055	15,051
CMBS
Amortized Cost
Amortized Cost	104,508	149,613
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	95,206	139,900
CMBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	104,508	149,613
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, Not Rated
Amortized Cost
Amortized Cost	$ 0	$ 0

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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