Securities (Securities available for sale) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,366,069	$ 1,659,456
Gross Unrealized Gains	16,205	11,423
Gross Unrealized Losses	(12,571)	(36,977)
Estimated Fair Value	1,369,703	1,633,902
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,361,048	1,654,460
Gross Unrealized Gains	16,157	11,391
Gross Unrealized Losses	(12,571)	(36,977)
Estimated Fair Value	1,364,634	1,628,874
U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,884	220,157
Gross Unrealized Gains	74	147
Gross Unrealized Losses	(12)	(2,001)
Estimated Fair Value	13,946	218,303
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,166,166	1,156,983
Gross Unrealized Gains	10,403	9,538
Gross Unrealized Losses	(11,692)	(22,574)
Estimated Fair Value	1,164,877	1,143,947
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	180,998	277,320
Gross Unrealized Gains	5,680	1,706
Gross Unrealized Losses	(867)	(12,402)
Estimated Fair Value	185,811	266,624
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,021	4,996
Gross Unrealized Gains	48	32
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 5,069	$ 5,028