Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	$ 11,017	$ 10,231
Less than 12 Months Fair Value	1,398,191	1,461,783
Less than 12 Months Unrealized Losses	(22,701)	(25,415)
12 Months or More Fair Value	161,992	165,173
12 Months or More Unrealized Losses	(6,106)	(5,276)
Total Fair Value	1,560,183	1,626,956
Total Unrealized Losses	(28,807)	(30,691)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	28,807	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	2,400	2,760
Less than 12 Months Fair Value	1,038,971	1,029,116
Less than 12 Months Unrealized Losses	(17,020)	(18,788)
12 Months or More Fair Value	155,846	159,046
12 Months or More Unrealized Losses	(5,796)	(4,930)
Total Fair Value	1,194,817	1,188,162
Total Unrealized Losses	(22,816)	(23,718)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	22,816	23,718
State and Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	7,316	6,343
Less than 12 Months Fair Value	162,860	211,342
Less than 12 Months Unrealized Losses	(4,249)	(5,064)
12 Months or More Fair Value	3,412	3,384
12 Months or More Unrealized Losses	(88)	(133)
Total Fair Value	166,272	214,726
Total Unrealized Losses	(4,337)	(5,197)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	4,337	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	1,241	1,065
Less than 12 Months Fair Value	193,846	218,811
Less than 12 Months Unrealized Losses	(1,381)	(1,511)
12 Months or More Fair Value	0	0
12 Months or More Unrealized Losses	0	0
Total Fair Value	193,846	218,811
Total Unrealized Losses	(1,381)	(1,511)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,381	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	251	251
Less than 12 Months Unrealized Losses	0	(1)
12 Months or More Fair Value	0	0
12 Months or More Unrealized Losses	0	0
Total Fair Value	251	251
Total Unrealized Losses	0	(1)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	1
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	60	63
Less than 12 Months Fair Value	2,263	2,263
Less than 12 Months Unrealized Losses	(51)	(51)
12 Months or More Fair Value	2,734	2,743
12 Months or More Unrealized Losses	(222)	(213)
Total Fair Value	4,997	5,006
Total Unrealized Losses	(273)	(264)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 273	$ 264