Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	$ 437,414	$ 887,693
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	2,350	23,148
12 Months or More Fair Value	561,668	166,348
12 Months or More Unrealized Losses	(11,989)	(15,783)
Total Fair Value	999,082	1,054,041
Total Unrealized Losses	(14,339)	(38,931)
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	258,825	492,921
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	1,287	10,991
12 Months or More Fair Value	279,015	121,303
12 Months or More Unrealized Losses	(6,924)	(12,684)
Total Fair Value	537,840	614,224
Total Unrealized Losses	(8,211)	(23,675)
State and Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	71,026	112,400
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	543	3,069
12 Months or More Fair Value	44,148	13,815
12 Months or More Unrealized Losses	(982)	(923)
Total Fair Value	115,174	126,215
Total Unrealized Losses	(1,525)	(3,992)
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	105,250	260,001
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	518	8,063
12 Months or More Fair Value	216,221	28,447
12 Months or More Unrealized Losses	(3,551)	(2,003)
Total Fair Value	321,471	288,448
Total Unrealized Losses	(4,069)	(10,066)
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	0	20,114
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	0	967
12 Months or More Fair Value	19,450	0
12 Months or More Unrealized Losses	(411)	0
Total Fair Value	19,450	20,114
Total Unrealized Losses	(411)	(967)
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	2,313	2,257
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant	2	58
12 Months or More Fair Value	2,834	2,783
12 Months or More Unrealized Losses	(121)	(173)
Total Fair Value	5,147	5,040
Total Unrealized Losses	$ (123)	$ (231)