Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	$ 63,945	$ 1,157,774
Less than 12 Months Unrealized Losses	(398)	(13,446)
12 Months or More Fair Value	72,174	521,420
12 Months or More Unrealized Losses	(1,381)	(6,994)
Total Fair Value	136,119	1,679,194
Total Unrealized Losses	(1,779)	(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	5,653	1,055,903
Less than 12 Months Unrealized Losses	(73)	(12,424)
12 Months or More Fair Value	69,916	491,539
12 Months or More Unrealized Losses	(1,375)	(6,798)
Total Fair Value	75,569	1,547,442
Total Unrealized Losses	(1,448)	(19,222)
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	15,105	89,508
Less than 12 Months Unrealized Losses	(44)	(880)
12 Months or More Fair Value	626	6,799
12 Months or More Unrealized Losses	(3)	(109)
Total Fair Value	15,731	96,307
Total Unrealized Losses	(47)	(989)
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	43,187	12,363
Less than 12 Months Unrealized Losses	(281)	(142)
12 Months or More Fair Value	1,632	12,587
12 Months or More Unrealized Losses	(3)	(82)
Total Fair Value	44,819	24,950
Total Unrealized Losses	$ (284)	(224)
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value		0
Less than 12 Months Unrealized Losses		0
12 Months or More Fair Value		10,495
12 Months or More Unrealized Losses		(5)
Total Fair Value		10,495
Total Unrealized Losses		$ (5)