Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value		$ 531,453	$ 276,306
Less than 12 Months Unrealized Losses		(4,272)	(1,598)
12 Months or More Fair Value		616,089	1,873,565
12 Months or More Unrealized Losses		(7,325)	(54,368)
Total Fair Value		1,147,542	2,149,871
Total Unrealized Losses		(11,597)	(55,966)
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	[1]	478,690	114,551
Less than 12 Months Unrealized Losses	[1]	(4,017)	(750)
12 Months or More Fair Value	[1]	528,228	1,207,020
12 Months or More Unrealized Losses	[1]	(7,045)	(40,096)
Total Fair Value	[1]	1,006,918	1,321,571
Total Unrealized Losses	[1]	(11,062)	(40,846)
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	[1]	0	40,071
Less than 12 Months Unrealized Losses	[1]	0	(222)
12 Months or More Fair Value	[1]	6,926	94,367
12 Months or More Unrealized Losses	[1]	(53)	(2,399)
Total Fair Value	[1]	6,926	134,438
Total Unrealized Losses	[1]	(53)	(2,621)
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value		52,763	106,292
Less than 12 Months Unrealized Losses		(255)	(581)
12 Months or More Fair Value		23,237	280,496
12 Months or More Unrealized Losses		(175)	(7,179)
Total Fair Value		76,000	386,788
Total Unrealized Losses		(430)	(7,760)
US Government Corporations and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value		0	15,392
Less than 12 Months Unrealized Losses		0	(45)
12 Months or More Fair Value		57,448	291,435
12 Months or More Unrealized Losses		(52)	(4,691)
Total Fair Value		57,448	306,827
Total Unrealized Losses		(52)	(4,736)
US Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value		0	0
Less than 12 Months Unrealized Losses		0	0
12 Months or More Fair Value		250	247
12 Months or More Unrealized Losses		0	(3)
Total Fair Value		250	247
Total Unrealized Losses		$ 0	$ (3)

[1] Beginning July 2019, other asset-backed securities were presented separately in this table. Prior period amounts that were previously reported in U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations have been reclassified to conform to current period presentation.