Investment Securities Available for Sale (Schedule Of Unrealized Loss On Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	$ 1,379,662	$ 891,914
Less than 12 Months, Gross Unrealized Losses	(16,669)	(2,468)
12 Months or Longer, Fair Value	0	5,309
12 Months or Longer, Gross Unrealized Losses	0	(38)
Total, Fair Value	1,379,662	897,223
Total, Gross Unrealized Losses	(16,669)	(2,506)
Gross Unrealized Gains	177,243	133,385
Gross Unrealized Losses	(16,669)	(2,506)
Investment securities available for sale, at fair value	7,962,438	6,778,670
Debt Securities, Available-for-sale, Amortized Cost	7,801,864	6,647,791
Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization	463,959	493,940
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available for sale, at fair value	20,257	19,855
Debt Securities, Available-for-sale, Amortized Cost	20,257	19,855
U.S. Government agency securities
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	2,682	1,042
Gross Unrealized Losses	0	0
Investment securities available for sale, at fair value	82,320	36,541
Debt Securities, Available-for-sale, Amortized Cost	79,638	35,499
Mortgage-backed securities issued by U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	566,896	19,543
Less than 12 Months, Gross Unrealized Losses	(5,925)	(70)
12 Months or Longer, Fair Value	0	355
12 Months or Longer, Gross Unrealized Losses	0	(2)
Total, Fair Value	566,896	19,898
Total, Gross Unrealized Losses	(5,925)	(72)
Gross Unrealized Gains	7,930	560
Gross Unrealized Losses	(5,925)	(72)
Investment securities available for sale, at fair value	1,218,017	56,816
Debt Securities, Available-for-sale, Amortized Cost	1,216,012	56,328
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value		768,040
Less than 12 Months, Gross Unrealized Losses		(2,076)
12 Months or Longer, Fair Value		0
12 Months or Longer, Gross Unrealized Losses		0
Total, Fair Value		768,040
Total, Gross Unrealized Losses		(2,076)
Gross Unrealized Gains	134,188	103,495
Gross Unrealized Losses	0	(2,076)
Investment securities available for sale, at fair value	5,000,046	5,180,815
Debt Securities, Available-for-sale, Amortized Cost	4,865,858	5,079,396
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	803,429	57,670
Less than 12 Months, Gross Unrealized Losses	(10,576)	(204)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total, Fair Value	803,429	57,670
Total, Gross Unrealized Losses	(10,576)	(204)
Gross Unrealized Gains	15,309	7,349
Gross Unrealized Losses	(10,576)	(204)
Investment securities available for sale, at fair value	1,250,377	636,851
Debt Securities, Available-for-sale, Amortized Cost	1,245,644	629,706
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	16,677	14,301
Gross Unrealized Losses	0	0
Investment securities available for sale, at fair value	370,921	371,592
Debt Securities, Available-for-sale, Amortized Cost	354,244	357,291
State and municipal securities
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains		6
Gross Unrealized Losses		0
Investment securities available for sale, at fair value		2,075
Debt Securities, Available-for-sale, Amortized Cost		2,069
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value		37,156
Less than 12 Months, Gross Unrealized Losses		(116)
12 Months or Longer, Fair Value		4,954
12 Months or Longer, Gross Unrealized Losses		(36)
Total, Fair Value		42,110
Total, Gross Unrealized Losses		(152)
Gross Unrealized Gains		4,315
Gross Unrealized Losses		(152)
Investment securities available for sale, at fair value		327,400
Debt Securities, Available-for-sale, Amortized Cost		323,237
Corporate debt securities and other debt securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	9,337	9,505
Less than 12 Months, Gross Unrealized Losses	(168)	(2)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total, Fair Value	9,337	9,505
Total, Gross Unrealized Losses	(168)	(2)
Gross Unrealized Gains	457	2,317
Gross Unrealized Losses	(168)	(2)
Investment securities available for sale, at fair value	20,500	146,725
Debt Securities, Available-for-sale, Amortized Cost	$ 20,211	$ 144,410

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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