Investment Securities (Summary Of Debt Securities Available-for-Sale) (Detail) $ in Thousands	Sep. 30, 2020 USD ($) numberOfHoldings	Dec. 31, 2019 USD ($) numberOfHoldings
Debt Securities, Available-for-sale [Abstract]
Amortized Cost(1)	$ 3,201,079	$ 2,901,415
Unrealized Gains	116,857	38,270
Unrealized Losses	(13,719)	(13,852)
Investment securities available-for-sale, at fair value	3,304,217	2,925,833
Interest receivable	56,600	59,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	518,360	607,521
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(10,465)	(1,914)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	69,003	762,631
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (3,254)	$ (11,938)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	78	157
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 587,363	$ 1,370,152
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(13,719)	(13,852)
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	0
Available-for-sale, Amortized Cost - Due after one year through five years	601
Available-for-sale, Amortized Cost - Due after five through ten years	263,579
Available-for-sale, Amortized Cost - Due after ten years	2,936,899
Available-for-sale, Amortized Cost - Total debt securities	3,201,079	2,901,415
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, Fair Value - Due in one year or less	0
Available-for-sale, Fair Value - Due after one year through five years	602
Available-for-sale, Fair Value - Due after five through ten years	257,909
Available-for-sale, Fair Value - Due after ten years	3,045,706
Debt Securities, Available-for-sale	3,304,217	2,925,833
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Interest receivable	7,400	8,100
Agency CMO [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost(1)	166,623	184,500
Unrealized Gains	6,908	2,218
Unrealized Losses	(177)	(917)
Investment securities available-for-sale, at fair value	173,354	185,801
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	11,358	36,447
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(92)	(352)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	7,935	32,288
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (85)	$ (565)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	3	9
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 19,293	$ 68,735
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(177)	(917)
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, Amortized Cost - Total debt securities	166,623	184,500
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Debt Securities, Available-for-sale	173,354	185,801
Agency MBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost(1)	1,446,100	1,580,743
Unrealized Gains	81,533	35,456
Unrealized Losses	(363)	(4,035)
Investment securities available-for-sale, at fair value	1,527,270	1,612,164
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	30,077	41,408
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(208)	(193)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	11,591	299,674
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (155)	$ (3,842)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	30	79
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 41,668	$ 341,082
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(363)	(4,035)
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, Amortized Cost - Total debt securities	1,446,100	1,580,743
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Debt Securities, Available-for-sale	1,527,270	1,612,164
Agency CMBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost(1)	1,024,133	587,974
Unrealized Gains	27,621	513
Unrealized Losses	0	(6,935)
Investment securities available-for-sale, at fair value	1,051,754	581,552
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		174,406
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(1,137)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		357,717
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		$ (5,798)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings		34
Debt Securities, Available-for-sale, Unrealized Loss Position		$ 532,123
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(6,935)
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, Amortized Cost - Total debt securities	1,024,133	587,974
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Debt Securities, Available-for-sale	1,051,754	581,552
Non-agency CMBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost(1)	464,071	432,085
Unrealized Gains	794	38
Unrealized Losses	(9,840)	(252)
Investment securities available-for-sale, at fair value	455,025	431,871
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	407,322	355,260
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(9,205)	(232)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	22,868	7,480
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (635)	$ (20)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	38	29
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 430,190	$ 362,740
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(9,840)	(252)
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, Amortized Cost - Total debt securities	464,071	432,085
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Debt Securities, Available-for-sale	455,025	431,871
CLO [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost(1)	85,601	92,628
Unrealized Gains	1	45
Unrealized Losses	(1,241)	(468)
Investment securities available-for-sale, at fair value	84,361	92,205
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	65,711
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(589)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	18,048	43,232
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (652)	$ (468)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	4	2
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 83,759	$ 43,232
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(1,241)	(468)
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, Amortized Cost - Total debt securities	85,601	92,628
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Debt Securities, Available-for-sale	84,361	92,205
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost(1)	14,551	23,485
Unrealized Gains	0	0
Unrealized Losses	(2,098)	(1,245)
Investment securities available-for-sale, at fair value	12,453	22,240
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	3,892
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(371)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	8,561	22,240
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (1,727)	$ (1,245)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	3	4
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 12,453	$ 22,240
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(2,098)	(1,245)
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, Amortized Cost - Total debt securities	14,551	23,485
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Debt Securities, Available-for-sale	$ 12,453	$ 22,240