Investment Securities Available for Sale (Schedule of Gross Unrealized Losses on Investment Securities and Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	$ 1,651,051	$ 891,914
Less than 12 Months, Gross Unrealized Losses	(11,393)	(2,468)
12 Months or Longer, Fair Value	0	5,309
12 Months or Longer, Gross Unrealized Losses	0	(38)
Total, Fair Value	1,651,051	897,223
Total, Gross Unrealized Losses	(11,393)	(2,506)
U.S. Government agency securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	48,921
Less than 12 Months, Gross Unrealized Losses	(426)
12 Months or Longer, Fair Value	0
12 Months or Longer, Gross Unrealized Losses	0
Total, Fair Value	48,921
Total, Gross Unrealized Losses	(426)
Mortgage-backed securities issued by U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	800,908	19,543
Less than 12 Months, Gross Unrealized Losses	(6,079)	(70)
12 Months or Longer, Fair Value	0	355
12 Months or Longer, Gross Unrealized Losses	0	(2)
Total, Fair Value	800,908	19,898
Total, Gross Unrealized Losses	(6,079)	(72)
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	180,899	768,040
Less than 12 Months, Gross Unrealized Losses	(276)	(2,076)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total, Fair Value	180,899	768,040
Total, Gross Unrealized Losses	(276)	(2,076)
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	609,208	57,670
Less than 12 Months, Gross Unrealized Losses	(4,222)	(204)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total, Fair Value	609,208	57,670
Total, Gross Unrealized Losses	(4,222)	(204)
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)
Corporate debt securities and other debt securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	11,115	9,505
Less than 12 Months, Gross Unrealized Losses	(390)	(2)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total, Fair Value	11,115	9,505
Total, Gross Unrealized Losses	$ (390)	$ (2)