Investment Securities (Summary Of Gross Unrealized Losses Not Considered OTTI) (Detail) $ in Thousands	Dec. 31, 2017 USD ($) holding	Dec. 31, 2016 USD ($) holding
Schedule of Investments [Line Items]
Available for Sale, Fair Value - Less Than Twelve Months	$ 650,514	$ 1,236,547
Available for sale, Unrealized Losses - Less Than Twelve Months	(4,869)	(27,316)
Available for sale, Fair Value - Twelve Months or Longer	1,265,234	470,314
Available for sale, Unrealized Losses - Twelve Months or Longer	$ (39,398)	$ (13,582)
Available for sale, Number of Holdings - Total | holding	212	168
Available for sale, Fair Value - Total	$ 1,915,748	$ 1,706,861
Available for sale, Unrealized Losses - Total	(44,267)	(40,898)
Held-to-maturity, Fair Value - Less Than Twelve Months	1,536,069	2,351,350
Held-to-maturity, Unrealized Losses - Less Than Twelve Months	(13,687)	(63,785)
Held-to-maturity, Fair Value - Twelve Months or Longer	1,655,375	292,225
Held-to-maturity, Unrealized Losses, Twelve Months or Longer	$ (45,768)	$ (9,315)
Held-to-maturity, Number of Holdings - Total | holding	388	395
Held-to-maturity, Fair Value - Total	$ 3,191,444	$ 2,643,575
Held-to-maturity, Unrealized Losses - Total	(59,455)	(73,100)
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Available for Sale, Fair Value - Less Than Twelve Months	81,001	107,853
Available for sale, Unrealized Losses - Less Than Twelve Months	(449)	(2,168)
Available for sale, Fair Value - Twelve Months or Longer	119,104	67,351
Available for sale, Unrealized Losses - Twelve Months or Longer	$ (3,365)	$ (1,335)
Available for sale, Number of Holdings - Total | holding	27	15
Available for sale, Fair Value - Total	$ 200,105	$ 175,204
Available for sale, Unrealized Losses - Total	(3,814)	(3,503)
Held-to-maturity, Fair Value - Less Than Twelve Months	98,090	163,439
Held-to-maturity, Unrealized Losses - Less Than Twelve Months	(1,082)	(3,339)
Held-to-maturity, Fair Value - Twelve Months or Longer	106,775	17,254
Held-to-maturity, Unrealized Losses, Twelve Months or Longer	$ (3,742)	$ (485)
Held-to-maturity, Number of Holdings - Total | holding	22	16
Held-to-maturity, Fair Value - Total	$ 204,865	$ 180,693
Held-to-maturity, Unrealized Losses - Total	(4,824)	(3,824)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Available for Sale, Fair Value - Less Than Twelve Months	416,995	512,075
Available for sale, Unrealized Losses - Less Than Twelve Months	(2,920)	(10,503)
Available for sale, Fair Value - Twelve Months or Longer	606,021	252,779
Available for sale, Unrealized Losses - Twelve Months or Longer	$ (16,350)	$ (9,006)
Available for sale, Number of Holdings - Total | holding	135	97
Available for sale, Fair Value - Total	$ 1,023,016	$ 764,854
Available for sale, Unrealized Losses - Total	(19,270)	(19,509)
Held-to-maturity, Fair Value - Less Than Twelve Months	762,107	1,394,623
Held-to-maturity, Unrealized Losses - Less Than Twelve Months	(4,555)	(32,942)
Held-to-maturity, Fair Value - Twelve Months or Longer	1,197,839	273,779
Held-to-maturity, Unrealized Losses, Twelve Months or Longer	$ (32,887)	$ (8,826)
Held-to-maturity, Number of Holdings - Total | holding	205	150
Held-to-maturity, Fair Value - Total	$ 1,959,946	$ 1,668,402
Held-to-maturity, Unrealized Losses - Total	(37,442)	(41,768)
Agency commercial mortgage-backed securities (agency CMBS) [Member]
Schedule of Investments [Line Items]
Available for Sale, Fair Value - Less Than Twelve Months	54,182	554,246
Available for sale, Unrealized Losses - Less Than Twelve Months	(851)	$ (14,567)
Available for sale, Fair Value - Twelve Months or Longer	533,844
Available for sale, Unrealized Losses - Twelve Months or Longer	$ (19,399)
Available for sale, Number of Holdings - Total | holding	36	32
Available for sale, Fair Value - Total	$ 588,026	$ 554,246
Available for sale, Unrealized Losses - Total	(20,250)	(14,567)
Held-to-maturity, Fair Value - Less Than Twelve Months	576,770	347,725
Held-to-maturity, Unrealized Losses - Less Than Twelve Months	(7,599)	$ (1,348)
Held-to-maturity, Fair Value - Twelve Months or Longer	109,785
Held-to-maturity, Unrealized Losses, Twelve Months or Longer	$ (2,412)
Held-to-maturity, Number of Holdings - Total | holding	56	25
Held-to-maturity, Fair Value - Total	$ 686,555	$ 347,725
Held-to-maturity, Unrealized Losses - Total	(10,011)	(1,348)
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available for Sale, Fair Value - Less Than Twelve Months	23,869	12,427
Available for sale, Unrealized Losses - Less Than Twelve Months	$ (74)	(24)
Available for sale, Fair Value - Twelve Months or Longer		63,930
Available for sale, Unrealized Losses - Twelve Months or Longer		$ (678)
Available for sale, Number of Holdings - Total | holding	6	12
Available for sale, Fair Value - Total	$ 23,869	$ 76,357
Available for sale, Unrealized Losses - Total	(74)	(702)
Held-to-maturity, Fair Value - Less Than Twelve Months	92,670	60,768
Held-to-maturity, Unrealized Losses - Less Than Twelve Months	(413)	$ (411)
Held-to-maturity, Fair Value - Twelve Months or Longer	14,115
Held-to-maturity, Unrealized Losses, Twelve Months or Longer	$ (207)
Held-to-maturity, Number of Holdings - Total | holding	13	8
Held-to-maturity, Fair Value - Total	$ 106,785	$ 60,768
Held-to-maturity, Unrealized Losses - Total	(620)	(411)
Collateralized loan obligations (CLO) [Member]
Schedule of Investments [Line Items]
Available for Sale, Fair Value - Less Than Twelve Months	56,335	49,946
Available for sale, Unrealized Losses - Less Than Twelve Months	$ (134)	(54)
Available for sale, Fair Value - Twelve Months or Longer		50,237
Available for sale, Unrealized Losses - Twelve Months or Longer		$ (465)
Available for sale, Number of Holdings - Total | holding	3	5
Available for sale, Fair Value - Total	$ 56,335	$ 100,183
Available for sale, Unrealized Losses - Total	(134)	(519)
Trust Preferred Securities Single Issuers [Member]
Schedule of Investments [Line Items]
Available for Sale, Fair Value - Less Than Twelve Months	7,050	0
Available for sale, Unrealized Losses - Less Than Twelve Months	$ (46)
Available for sale, Fair Value - Twelve Months or Longer		28,633
Available for sale, Unrealized Losses - Twelve Months or Longer		$ (1,748)
Available for sale, Number of Holdings - Total | holding	1	5
Available for sale, Fair Value - Total	$ 7,050	$ 28,633
Available for sale, Unrealized Losses - Total	(46)	(1,748)
Municipal Bonds [Member]
Schedule of Investments [Line Items]
Held-to-maturity, Fair Value - Less Than Twelve Months	6,432	384,795
Held-to-maturity, Unrealized Losses - Less Than Twelve Months	(38)	(25,745)
Held-to-maturity, Fair Value - Twelve Months or Longer	226,861	1,192
Held-to-maturity, Unrealized Losses, Twelve Months or Longer	$ (6,520)	$ (4)
Held-to-maturity, Number of Holdings - Total | holding	92	196
Held-to-maturity, Fair Value - Total	$ 233,293	$ 385,987
Held-to-maturity, Unrealized Losses - Total	(6,558)	(25,749)
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available for Sale, Fair Value - Less Than Twelve Months	11,082
Available for sale, Unrealized Losses - Less Than Twelve Months	(395)
Available for sale, Fair Value - Twelve Months or Longer	6,265	7,384
Available for sale, Unrealized Losses - Twelve Months or Longer	$ (284)	$ (350)
Available for sale, Number of Holdings - Total | holding	4	2
Available for sale, Fair Value - Total	$ 17,347	$ 7,384
Available for sale, Unrealized Losses - Total	$ (679)	$ (350)