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Investment Securities Available for Sale (Summary Of Available For Sale Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 7,801,864	$ 6,647,791
Gross Unrealized Gains	177,243	133,385
Gross Unrealized Losses	(16,669)	(2,506)
Fair Value	7,962,438	6,778,670
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	20,257	19,855
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	20,257	19,855
U.S. Government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	79,638	35,499
Gross Unrealized Gains	2,682	1,042
Gross Unrealized Losses	0	0
Fair Value	82,320	36,541
Mortgage-backed securities issued by U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,216,012	56,328
Gross Unrealized Gains	7,930	560
Gross Unrealized Losses	(5,925)	(72)
Fair Value	1,218,017	56,816
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,865,858	5,079,396
Gross Unrealized Gains	134,188	103,495
Gross Unrealized Losses	0	(2,076)
Fair Value	5,000,046	5,180,815
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,245,644	629,706
Gross Unrealized Gains	15,309	7,349
Gross Unrealized Losses	(10,576)	(204)
Fair Value	1,250,377	636,851
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	354,244	357,291
Gross Unrealized Gains	16,677	14,301
Gross Unrealized Losses	0	0
Fair Value	370,921	371,592
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		323,237
Gross Unrealized Gains		4,315
Gross Unrealized Losses		(152)
Fair Value		327,400
Corporate debt securities and other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	20,211	144,410
Gross Unrealized Gains	457	2,317
Gross Unrealized Losses	(168)	(2)
Fair Value	$ 20,500	$ 146,725

X

- Definition

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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