Securities (Summary of Gross Unrealized Losses and Fair Value of Debt Securities Available-for-Sale with Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	$ 880,507	$ 1,157,774
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	(6,453)	(13,446)
12 Months or More Fair Value	18,597	521,420
12 Months or More Unrealized Losses	(815)	(6,994)
Total Fair Value	899,104	1,679,194
Total Unrealized losses	7,268	20,440
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	575,329	1,055,903
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	(3,728)	(12,424)
12 Months or More Fair Value	18,527	491,539
12 Months or More Unrealized Losses	(815)	(6,798)
Total Fair Value	593,856	1,547,442
Total Unrealized losses	4,543	19,222
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	143,764	89,508
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	(2,076)	(880)
12 Months or More Fair Value	70	6,799
12 Months or More Unrealized Losses	0	(109)
Total Fair Value	143,834	96,307
Total Unrealized losses	2,076	989
State and Municipal Securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	86,471	12,363
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	(592)	(142)
12 Months or More Fair Value	0	12,587
12 Months or More Unrealized Losses	0	(82)
Total Fair Value	86,471	24,950
Total Unrealized losses	592	224
U.S. Government Agency and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	74,943	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	(57)	0
12 Months or More Fair Value	0	10,495
12 Months or More Unrealized Losses	0	(5)
Total Fair Value	74,943	10,495
Total Unrealized losses	$ 57	$ 5