Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	$ 580,986	$ 1,157,774
Less than 12 Months Unrealized Losses	(4,212)	(13,446)
12 Months or More Fair Value	23,179	521,420
12 Months or More Unrealized Losses	(840)	(6,994)
Total Fair Value	604,165	1,679,194
Total Unrealized Losses	(5,052)	(20,440)
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	318,868	1,055,903
Less than 12 Months Unrealized Losses	(2,817)	(12,424)
12 Months or More Fair Value	23,084	491,539
12 Months or More Unrealized Losses	(840)	(6,798)
Total Fair Value	341,952	1,547,442
Total Unrealized Losses	(3,657)	(19,222)
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	71,552	89,508
Less than 12 Months Unrealized Losses	(530)	(880)
12 Months or More Fair Value	95	6,799
12 Months or More Unrealized Losses	0	(109)
Total Fair Value	71,647	96,307
Total Unrealized Losses	(530)	(989)
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	90,620	12,363
Less than 12 Months Unrealized Losses	(813)	(142)
12 Months or More Fair Value	0	12,587
12 Months or More Unrealized Losses	0	(82)
Total Fair Value	90,620	24,950
Total Unrealized Losses	(813)	(224)
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	99,946	0
Less than 12 Months Unrealized Losses	(52)	0
12 Months or More Fair Value	0	10,495
12 Months or More Unrealized Losses	0	(5)
Total Fair Value	99,946	10,495
Total Unrealized Losses	$ (52)	$ (5)