Investment Securities (Summary Of Debt Securities Held-to Maturity) (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Held-to-maturity, Amortized Cost - Due in one year or less	$ 1,085
Held-to-maturity, Amortized Cost - Due after one year through five years	5,340
Held-to-maturity, Amortized Cost - Due after five through ten years	279,056
Held-to-maturity, Amortized Cost - Due after ten years	5,437,953
Amortized Cost(1)	5,723,434	$ 5,293,918
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held to maturity, Fair Value - Due in one year or less	1,089
Held-to-maturity, Fair Value - Due after one year through five years	5,611
Held to maturity, Fair Value - Due after five through ten years	295,103
Held to maturity, Fair Value - Due after ten years	5,704,613
Fair Value(2)	6,006,416	5,380,653
Moody's, Aaa Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	436,781
Moody's, Aa1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	4,910,818
Moody's, Aa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	201,423
Moody's, Aa3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	117,320
Moody's, A1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	41,697
Moody's, A2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	8,663
Moody's, A3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,066
Moody's, Baa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	285
Moody's, Not Rated
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	4,381
Agency CMO [Member]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	116,020	167,443
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	118,502	167,366
Agency CMO [Member] | Moody's, Aaa Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMO [Member] | Moody's, Aa1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	116,020
Agency CMO [Member] | Moody's, Aa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMO [Member] | Moody's, Aa3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMO [Member] | Moody's, A1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMO [Member] | Moody's, A2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMO [Member] | Moody's, A3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMO [Member] | Moody's, Baa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMO [Member] | Moody's, Not Rated
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,595,711	2,957,900
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	2,750,826	3,009,769
Agency MBS [Member] | Moody's, Aaa Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member] | Moody's, Aa1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,595,711
Agency MBS [Member] | Moody's, Aa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member] | Moody's, Aa3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member] | Moody's, A1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member] | Moody's, A2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member] | Moody's, A3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member] | Moody's, Baa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member] | Moody's, Not Rated
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,033,826	1,172,491
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	2,096,628	1,173,320
Agency CMBS [Member] | Moody's, Aaa Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member] | Moody's, Aa1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,033,826
Agency CMBS [Member] | Moody's, Aa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member] | Moody's, Aa3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member] | Moody's, A1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member] | Moody's, A2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member] | Moody's, A3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member] | Moody's, Baa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member] | Moody's, Not Rated
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Municipal bonds and notes [Member]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	750,847	740,431
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	804,304	773,119
Municipal bonds and notes [Member] | Moody's, Aaa Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	209,751
Municipal bonds and notes [Member] | Moody's, Aa1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	165,261
Municipal bonds and notes [Member] | Moody's, Aa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	201,423
Municipal bonds and notes [Member] | Moody's, Aa3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	117,320
Municipal bonds and notes [Member] | Moody's, A1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	41,697
Municipal bonds and notes [Member] | Moody's, A2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	8,663
Municipal bonds and notes [Member] | Moody's, A3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,066
Municipal bonds and notes [Member] | Moody's, Baa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	285
Municipal bonds and notes [Member] | Moody's, Not Rated
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	4,381
Non-agency CMBS [Member]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	227,030	255,653
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	236,156	$ 257,079
Non-agency CMBS [Member] | Moody's, Aaa Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	227,030
Non-agency CMBS [Member] | Moody's, Aa1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Non-agency CMBS [Member] | Moody's, Aa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Non-agency CMBS [Member] | Moody's, Aa3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Non-agency CMBS [Member] | Moody's, A1 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Non-agency CMBS [Member] | Moody's, A2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Non-agency CMBS [Member] | Moody's, A3 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Non-agency CMBS [Member] | Moody's, Baa2 Rating
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Non-agency CMBS [Member] | Moody's, Not Rated
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	$ 0