Investment Securities (Summary Of Debt Securities Held-to Maturity - Contractual Maturities, Credit Quality and Other Information) (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Amortized Cost
Maturing within 1 year	$ 29,846
After 1 year through 5 years	94,598
After 5 through 10 years	299,712
After 10 years	7,255,919
Amortized Cost	7,680,075	$ 7,074,797
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Maturing within 1 year	29,771
After 1 year through 5 years	89,326
After 5 through 10 years	288,067
After 10 years	6,375,703
Fair Value	6,782,867	6,264,623
Held-to-maturity securities pledged	7,290,556	6,795,203
Moody's, Aaa Rating
Amortized Cost
Amortized Cost	432,551	433,554
Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	6,832,510	6,221,233
Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	252,852	253,671
Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	111,277	115,404
Moody's, A1 Rating
Amortized Cost
Amortized Cost	32,690	32,732
Moody's, A3 Rating
Amortized Cost
Amortized Cost	4,165	4,165
Moody's, Not Rated
Amortized Cost
Amortized Cost	14,030	14,038
Pledged For Municipal Deposits
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity securities pledged	1,557,987	1,212,824
Pledged For Borrowings
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity securities pledged	5,732,569	5,582,379
Agency CMO
Amortized Cost
Amortized Cost	22,489	23,470
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	20,551	21,742
Agency CMO \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency CMO \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	22,489	23,470
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, 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	2,618,783	2,409,521
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	2,292,861	2,125,886
Agency MBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency MBS \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	2,618,783	2,409,521
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, 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	4,028,799	3,625,627
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	3,499,738	3,129,679
Agency CMBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	0	0
Agency CMBS \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	4,028,799	3,625,627
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, 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	910,422	916,104
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	876,152	893,667
Municipal bonds and notes \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	332,969	333,479
Municipal bonds and notes \| Moody's, Aa1 Rating
Amortized Cost
Amortized Cost	162,439	162,615
Municipal bonds and notes \| Moody's, Aa2 Rating
Amortized Cost
Amortized Cost	252,852	253,671
Municipal bonds and notes \| Moody's, Aa3 Rating
Amortized Cost
Amortized Cost	111,277	115,404
Municipal bonds and notes \| Moody's, A1 Rating
Amortized Cost
Amortized Cost	32,690	32,732
Municipal bonds and notes \| Moody's, A3 Rating
Amortized Cost
Amortized Cost	4,165	4,165
Municipal bonds and notes \| Moody's, Not Rated
Amortized Cost
Amortized Cost	14,030	14,038
CMBS
Amortized Cost
Amortized Cost	99,582	100,075
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value	93,565	93,649
CMBS \| Moody's, Aaa Rating
Amortized Cost
Amortized Cost	99,582	100,075
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, 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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