Securities (Securities available for sale) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,405,816	$ 1,659,456
Gross Unrealized Gains	12,609	11,423
Gross Unrealized Losses	(17,669)	(36,977)
Estimated Fair Value	1,400,756	1,633,902
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,400,811	1,654,460
Gross Unrealized Gains	12,573	11,391
Gross Unrealized Losses	(17,669)	(36,977)
Estimated Fair Value	1,395,715	1,628,874
U.S. Government Corporations and Agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	147,350	220,157
Gross Unrealized Gains	115	147
Gross Unrealized Losses	(769)	(2,001)
Estimated Fair Value	146,696	218,303
Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,052,695	1,156,983
Gross Unrealized Gains	10,035	9,538
Gross Unrealized Losses	(13,109)	(22,574)
Estimated Fair Value	1,049,621	1,143,947
Obligations of States and Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	200,766	277,320
Gross Unrealized Gains	2,423	1,706
Gross Unrealized Losses	(3,791)	(12,402)
Estimated Fair Value	199,398	266,624
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,005	4,996
Gross Unrealized Gains	36	32
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 5,041	$ 5,028