Investment Securities (Summary Of Gross Unrealized Losses Not Considered OTTI) (Detail) $ in Thousands	Dec. 31, 2019 USD ($) numberOfHoldings	Dec. 31, 2018 USD ($) numberOfHoldings
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 607,521	$ 799,954
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,914)	(8,602)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	762,631	1,756,617
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (11,938)	$ (90,067)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	157	309
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 1,370,152	$ 2,556,571
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(13,852)	(98,669)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	766,770	382,558
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	7,803	3,069
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	786,528	3,257,871
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 8,618	$ 125,132
Held-to-maturity, Number of Holdings - Total | numberOfHoldings	146	596
Held-to-maturity, Fair Value - Total	$ 1,553,298	$ 3,640,429
Held-to-maturity, Unrealized Losses - Total	(16,421)	(128,201)
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	36,447	15,524
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(352)	(72)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	32,288	180,641
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (565)	$ (4,385)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	9	36
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 68,735	$ 196,165
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(917)	(4,457)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	26,480	691
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	174	1
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	54,602	182,396
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 1,026	$ 5,254
Held-to-maturity, Number of Holdings - Total | numberOfHoldings	11	25
Held-to-maturity, Fair Value - Total	$ 81,082	$ 183,087
Held-to-maturity, Unrealized Losses - Total	(1,200)	(5,255)
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	41,408	321,678
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(193)	(2,078)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	299,674	975,084
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (3,842)	$ (39,998)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	79	184
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 341,082	$ 1,296,762
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(4,035)	(42,076)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	164,269	288,635
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,165	1,916
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	727,778	1,892,951
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 7,568	$ 77,785
Held-to-maturity, Number of Holdings - Total | numberOfHoldings	105	272
Held-to-maturity, Fair Value - Total	$ 892,047	$ 2,181,586
Held-to-maturity, Unrealized Losses - Total	(8,733)	(79,701)
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	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	566,237
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (5,798)	$ (41,930)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	34	37
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 532,123	$ 566,237
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(6,935)	(41,930)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	488,091
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,591
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	4,148	635,284
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 24	$ 22,572
Held-to-maturity, Number of Holdings - Total | numberOfHoldings	21	56
Held-to-maturity, Fair Value - Total	$ 492,239	$ 635,284
Held-to-maturity, Unrealized Losses - Total	(5,615)	(22,572)
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	355,260	343,457
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(232)	(2,937)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	7,480	5,193
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (20)	$ (24)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	29	39
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 362,740	$ 348,650
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(252)	(2,961)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	85,422	24,881
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 852	270
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value		132,464
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		$ 2,118
Held-to-maturity, Number of Holdings - Total | numberOfHoldings	8	20
Held-to-maturity, Fair Value - Total	$ 85,422	$ 157,345
Held-to-maturity, Unrealized Losses - Total	(852)	(2,388)
Collateralized loan obligations (CLO) [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		83,305
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(1,695)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	43,232	14,873
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (468)	$ (269)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	2	5
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 43,232	$ 98,178
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(468)	(1,964)
Municipal Bonds [Member]
Schedule of Investments [Line Items]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	2,508	68,351
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 21	882
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value		414,776
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		$ 17,403
Held-to-maturity, Number of Holdings - Total | numberOfHoldings	1	223
Held-to-maturity, Fair Value - Total	$ 2,508	$ 483,127
Held-to-maturity, Unrealized Losses - Total	(21)	(18,285)
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		35,990
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(1,820)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	22,240	14,589
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (1,245)	$ (3,461)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | numberOfHoldings	4	8
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 22,240	$ 50,579
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (1,245)	$ (5,281)