Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	$ 13,644	$ 10,231
Less than 12 Months Fair Value	788,216	1,461,783
Less than 12 Months Unrealized Losses	(6,167)	(25,415)
12 Months or More Fair Value	525,915	165,173
12 Months or More Unrealized Losses	(14,939)	(5,276)
Total Fair Value	1,314,131	1,626,956
Total Unrealized Losses	(21,106)	(30,691)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	21,106	30,691
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	3,143	2,760
Less than 12 Months Fair Value	537,162	1,029,116
Less than 12 Months Unrealized Losses	(4,765)	(18,788)
12 Months or More Fair Value	456,330	159,046
12 Months or More Unrealized Losses	(12,597)	(4,930)
Total Fair Value	993,492	1,188,162
Total Unrealized Losses	(17,362)	(23,718)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	17,362	23,718
State and Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	9,047	6,343
Less than 12 Months Fair Value	75,499	211,342
Less than 12 Months Unrealized Losses	(700)	(5,064)
12 Months or More Fair Value	45,328	3,384
12 Months or More Unrealized Losses	(1,561)	(133)
Total Fair Value	120,827	214,726
Total Unrealized Losses	(2,261)	(5,197)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2,261	5,197
US Government Corporations and Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	1,372	1,065
Less than 12 Months Fair Value	173,027	218,811
Less than 12 Months Unrealized Losses	(665)	(1,511)
12 Months or More Fair Value	21,517	0
12 Months or More Unrealized Losses	(565)	0
Total Fair Value	194,544	218,811
Total Unrealized Losses	(1,230)	(1,511)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,230	1,511
US Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	0	0
Less than 12 Months Fair Value	250	251
Less than 12 Months Unrealized Losses	(1)	(1)
12 Months or More Fair Value	0	0
12 Months or More Unrealized Losses	0	0
Total Fair Value	250	251
Total Unrealized Losses	(1)	(1)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1	1
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	82	63
Less than 12 Months Fair Value	2,278	2,263
Less than 12 Months Unrealized Losses	(36)	(51)
12 Months or More Fair Value	2,740	2,743
12 Months or More Unrealized Losses	(216)	(213)
Total Fair Value	5,018	5,006
Total Unrealized Losses	(252)	(264)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 252	$ 264