Investment Securities Available for Sale (Schedule of Gross Unrealized Losses on Investment Securities and Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	$ 4,315,642	$ 1,379,662
Less than 12 Months, Gross Unrealized Losses	(55,229)	(16,669)
12 Months or Longer, Fair Value	294,264	0
12 Months or Longer, Gross Unrealized Losses	(4,113)	0
Total, Fair Value	4,609,906	1,379,662
Total, Gross Unrealized Losses	(59,342)	(16,669)
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	47,586
Less than 12 Months, Gross Unrealized Losses	(2,243)
12 Months or Longer, Fair Value	0
12 Months or Longer, Gross Unrealized Losses	0
Total, Fair Value	47,586
Total, Gross Unrealized Losses	(2,243)
Mortgage-backed securities issued by U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	421,704	566,896
Less than 12 Months, Gross Unrealized Losses	(5,251)	(5,925)
12 Months or Longer, Fair Value	153,330	0
12 Months or Longer, Gross Unrealized Losses	(1,826)	0
Total, Fair Value	575,034	566,896
Total, Gross Unrealized Losses	(7,077)	(5,925)
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	3,156,297
Less than 12 Months, Gross Unrealized Losses	(37,855)
12 Months or Longer, Fair Value	0
12 Months or Longer, Gross Unrealized Losses	0
Total, Fair Value	3,156,297
Total, Gross Unrealized Losses	(37,855)
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	524,044	803,429
Less than 12 Months, Gross Unrealized Losses	(6,858)	(10,576)
12 Months or Longer, Fair Value	140,934	0
12 Months or Longer, Gross Unrealized Losses	(2,287)	0
Total, Fair Value	664,978	803,429
Total, Gross Unrealized Losses	(9,145)	(10,576)
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	166,011
Less than 12 Months, Gross Unrealized Losses	(3,022)
12 Months or Longer, Fair Value	0
12 Months or Longer, Gross Unrealized Losses	0
Total, Fair Value	166,011
Total, Gross Unrealized Losses	$ (3,022)
Corporate debt securities and other debt securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value		9,337
Less than 12 Months, Gross Unrealized Losses		(168)
12 Months or Longer, Fair Value		0
12 Months or Longer, Gross Unrealized Losses		0
Total, Fair Value		9,337
Total, Gross Unrealized Losses		$ (168)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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