Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Equity Securities, FV-NI, Gain (Loss)	$ 195	$ 0	$ 0
Equity Securities, FV-NI, Realized Gain (Loss)	(195)
Less than 12 Months Fair Value	276,306	1,220,992
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	1,598	9,442
12 Months or More Fair Value	1,873,565	948,366
12 Months or More Unrealized Losses	(54,368)	(24,608)
Total Fair Value	2,149,871	2,169,358
Total Unrealized Losses	(55,966)	(34,050)
Equity Securities, FV-NI, Unrealized Gain (Loss)	0
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	154,622	816,678
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	972	6,710
12 Months or More Fair Value	1,301,387	717,211
12 Months or More Unrealized Losses	(42,495)	(20,616)
Total Fair Value	1,456,009	1,533,889
Total Unrealized Losses	(43,467)	(27,326)
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	106,292	220,019
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	581	1,723
12 Months or More Fair Value	280,496	75,172
12 Months or More Unrealized Losses	(7,179)	(2,236)
Total Fair Value	386,788	295,191
Total Unrealized Losses	(7,760)	(3,959)
U.S. Government Agency and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	15,392	184,046
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	45	1,006
12 Months or More Fair Value	291,435	155,983
12 Months or More Unrealized Losses	(4,691)	(1,756)
Total Fair Value	306,827	340,029
Total Unrealized Losses	(4,736)	(2,762)
US Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months Fair Value	0	249
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	0	3
12 Months or More Fair Value	247	0
12 Months or More Unrealized Losses	(3)	0
Total Fair Value	247	249
Total Unrealized Losses	$ (3)	$ (3)