Investment Securities (Summary Of Gross Unrealized Losses Not Considered OTTI) (Detail) $ in Thousands	Dec. 31, 2020 USD ($) numberOfHoldings	Dec. 31, 2019 USD ($) numberOfHoldings
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 894,628	$ 607,521
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(7,699)	(1,914)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	61,347	762,631
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (1,772)	$ (11,938)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	88	157
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 955,975	$ 1,370,152
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(9,471)	(13,852)
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	13,137	36,447
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(49)	(352)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	5,944	32,288
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (49)	$ (565)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	5	9
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 19,081	$ 68,735
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(98)	(917)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	33,742	41,408
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(219)	(193)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4,561	299,674
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (70)	$ (3,842)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	30	79
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 38,303	$ 341,082
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(289)	(4,035)
Agency commercial mortgage-backed securities (agency CMBS) [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	376,330	174,406
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,514)	(1,137)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	357,717
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0	$ (5,798)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	8	34
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 376,330	$ 532,123
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(1,514)	(6,935)
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	409,591	355,260
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(5,486)	(232)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	23,167	7,480
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (337)	$ (20)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	38	29
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 432,758	$ 362,740
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(5,823)	(252)
Collateralized loan obligations (CLO) [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	57,728	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(265)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	18,655	43,232
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (45)	$ (468)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	4	2
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 76,383	$ 43,232
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(310)	(468)
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	4,100	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(166)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	9,020	22,240
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (1,271)	$ (1,245)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	3	4
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 13,120	$ 22,240
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (1,437)	$ (1,245)