Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	$ 1,461,783	$ 918,813
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	25,415	9,247
12 Months or More Fair Value	165,173	298,316
12 Months or More Unrealized Losses	(5,276)	(9,021)
Total Fair Value	1,626,956	1,217,129
Total Unrealized Losses	(30,691)	(18,268)
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	1,029,116	664,509
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	18,788	7,610
12 Months or More Fair Value	159,046	214,325
12 Months or More Unrealized Losses	(4,930)	(7,381)
Total Fair Value	1,188,162	878,834
Total Unrealized Losses	(23,718)	(14,991)
State and Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	211,342	48,261
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	5,064	358
12 Months or More Fair Value	3,384	31,383
12 Months or More Unrealized Losses	(133)	(580)
Total Fair Value	214,726	79,644
Total Unrealized Losses	(5,197)	(938)
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	218,811	193,400
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	1,511	1,128
12 Months or More Fair Value	0	40,034
12 Months or More Unrealized Losses	0	(718)
Total Fair Value	218,811	233,434
Total Unrealized Losses	(1,511)	(1,846)
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	251	10,343
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	1	136
12 Months or More Fair Value	0	9,794
12 Months or More Unrealized Losses	0	(166)
Total Fair Value	251	20,137
Total Unrealized Losses	(1)	(302)
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	2,263	2,300
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	51	15
12 Months or More Fair Value	2,743	2,780
12 Months or More Unrealized Losses	(213)	(176)
Total Fair Value	5,006	5,080
Total Unrealized Losses	$ (264)	$ (191)