Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	$ 1,413,001	$ 880,507
Less than 12 Months Unrealized Losses	(16,707)	(6,453)
12 Months or More Fair Value	25,010	18,597
12 Months or More Unrealized Losses	(402)	(815)
Total Fair Value	1,438,011	899,104
Total Unrealized Losses	(17,109)	(7,268)
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	807,523	575,329
Less than 12 Months Unrealized Losses	(8,956)	(3,728)
12 Months or More Fair Value	23,308	18,527
12 Months or More Unrealized Losses	(386)	(815)
Total Fair Value	830,831	593,856
Total Unrealized Losses	(9,342)	(4,543)
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	232,155	143,764
Less than 12 Months Unrealized Losses	(3,976)	(2,076)
12 Months or More Fair Value	55	70
12 Months or More Unrealized Losses	0	0
Total Fair Value	232,210	143,834
Total Unrealized Losses	(3,976)	(2,076)
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	223,105	86,471
Less than 12 Months Unrealized Losses	(2,443)	(592)
12 Months or More Fair Value	1,647	0
12 Months or More Unrealized Losses	(15)	0
Total Fair Value	224,752	86,471
Total Unrealized Losses	(2,458)	(592)
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	150,218	74,943
Less than 12 Months Unrealized Losses	(1,332)	(57)
12 Months or More Fair Value	0	0
12 Months or More Unrealized Losses	(1)	0
Total Fair Value	150,218	74,943
Total Unrealized Losses	$ (1,333)	$ (57)