Investment Securities (Summary Of Debt Securities Held-to Maturity) (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	$ 5,486,206	$ 5,293,918
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(1,744)	(16,421)
Debt Securities, Held-to-maturity, Fair Value	5,642,527	5,380,653
Allowance for credit losses on investment securities held-to-maturity	312	0
Net Carrying Value	5,485,894	5,293,918
Investment securities available-for-sale, at fair value	3,016,631	2,925,833
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	1,084
Held-to-maturity, Amortized Cost - Due after one year through five years	5,273
Held-to-maturity, Amortized Cost - Due after five through ten years	266,866
Held-to-maturity, Amortized Cost - Due after ten years	5,212,983
Amortized Cost(1)	5,486,206	5,293,918
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held to maturity, Fair Value - Due in one year or less	1,088
Held-to-maturity, Fair Value - Due after one year through five years	5,452
Held to maturity, Fair Value - Due after five through ten years	274,217
Held to maturity, Fair Value - Due after ten years	5,361,770
Fair Value(2)	5,642,527	5,380,653
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	5,486,206	5,293,918
Unrealized Gains	158,065	103,156
Fair Value(2)	5,642,527	5,380,653
Allowance for credit losses on investment securities held-to-maturity	312	0
Net Carrying Value	5,485,894	5,293,918
Moody's, Aaa Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	453,633
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	453,633
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	453,633
Moody's, Aa1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	4,643,040
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	4,643,040
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	4,643,040
Moody's, Aa2 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	207,227
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	207,227
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	207,227
Moody's, Aa3 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	126,623
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	126,623
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	126,623
Moody's, A1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	42,265
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	42,265
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	42,265
Moody's, A2 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	8,671
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	8,671
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	8,671
Moody's, A3 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	2,066
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,066
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	2,066
Moody's, Baa2 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	285
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	285
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	285
Moody's, B1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	2,396
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,396
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	2,396
Agency CMO [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	156,087	167,443
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	0	(1,200)
Debt Securities, Held-to-maturity, Fair Value	160,825	167,366
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	156,087	167,443
Investment securities available-for-sale, at fair value	204,830	185,801
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	156,087	167,443
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	160,825	167,366
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	156,087	167,443
Unrealized Gains	4,738	1,123
Fair Value(2)	160,825	167,366
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	156,087	167,443
Agency CMO [Member] | Moody's, Aaa Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMO [Member] | Moody's, Aa1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	156,087
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	156,087
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	156,087
Agency MBS [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	2,896,651	2,957,900
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(253)	(8,733)
Debt Securities, Held-to-maturity, Fair Value	2,991,834	3,009,769
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	2,896,651	2,957,900
Investment securities available-for-sale, at fair value	1,612,818	1,612,164
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,896,651	2,957,900
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	2,991,834	3,009,769
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	2,896,651	2,957,900
Unrealized Gains	95,436	60,602
Fair Value(2)	2,991,834	3,009,769
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	2,896,651	2,957,900
Agency MBS [Member] | Moody's, Aaa Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency MBS [Member] | Moody's, Aa1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	2,896,651
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,896,651
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	2,896,651
Agency CMBS [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	1,450,800	1,172,491
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(623)	(5,615)
Debt Securities, Held-to-maturity, Fair Value	1,471,180	1,173,320
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	1,450,800	1,172,491
Investment securities available-for-sale, at fair value	697,682	581,552
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	1,450,800	1,172,491
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	1,471,180	1,173,320
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	1,450,800	1,172,491
Unrealized Gains	21,003	6,444
Fair Value(2)	1,471,180	1,173,320
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	1,450,800	1,172,491
Agency CMBS [Member] | Moody's, Aaa Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	0
Agency CMBS [Member] | Moody's, Aa1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	1,450,800
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	1,450,800
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	1,450,800
Municipal bonds and notes [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	739,531	740,431
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(86)	(21)
Debt Securities, Held-to-maturity, Fair Value	774,629	773,119
Allowance for credit losses on investment securities held-to-maturity	312	0
Net Carrying Value	739,219	740,431
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	739,531	740,431
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	774,629	773,119
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	739,531	740,431
Unrealized Gains	35,184	32,709
Fair Value(2)	774,629	773,119
Allowance for credit losses on investment securities held-to-maturity	312	0
Net Carrying Value	739,219	740,431
Municipal bonds and notes [Member] | Moody's, Aaa Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	210,496
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	210,496
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	210,496
Municipal bonds and notes [Member] | Moody's, Aa1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	139,502
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	139,502
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	139,502
Municipal bonds and notes [Member] | Moody's, Aa2 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	207,227
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	207,227
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	207,227
Municipal bonds and notes [Member] | Moody's, Aa3 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	126,623
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	126,623
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	126,623
Municipal bonds and notes [Member] | Moody's, A1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	42,265
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	42,265
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	42,265
Municipal bonds and notes [Member] | Moody's, A2 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	8,671
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	8,671
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	8,671
Municipal bonds and notes [Member] | Moody's, A3 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	2,066
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,066
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	2,066
Municipal bonds and notes [Member] | Moody's, Baa2 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	285
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	285
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	285
Municipal bonds and notes [Member] | Moody's, B1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	2,396
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	2,396
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	2,396
Non-agency CMBS [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	243,137	255,653
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(782)	(852)
Debt Securities, Held-to-maturity, Fair Value	244,059	257,079
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	243,137	255,653
Investment securities available-for-sale, at fair value	409,023	431,871
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	243,137	255,653
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Fair Value(2)	244,059	257,079
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	243,137	255,653
Unrealized Gains	1,704	2,278
Fair Value(2)	244,059	257,079
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	243,137	255,653
Non-agency CMBS [Member] | Moody's, Aaa Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	243,137
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	243,137
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	243,137
Non-agency CMBS [Member] | Moody's, Aa1 Rating
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized Cost(1)	0
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost(1)	0
CLO [Member]
Schedule of Investments [Line Items]
Investment securities available-for-sale, at fair value	81,398	92,205
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Investment securities available-for-sale, at fair value	$ 10,880	$ 22,240