Investment Securities (Narrative) (Details Textual) (USD $)	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Schedule of Investments [Line Items]
Available for sale securities, net unrealized losses	$ (15,600,000)	$ (55,900,000)	$ (12,400,000)
Number of states with aggregate fair value of general obligation bonds greater than $10 million	11
Available-for-sale Securities, Gross Unrealized Loss at End of Period	56,396,000	90,220,000	57,197,000
Number of Single Issuer Trust Preferred Securities With Stated Maturities	8
Percent of trust preferred securities included in fair value of entire investment portfolio	2.00%
Available-for-sale	3,478,420,000	3,273,174,000	3,299,392,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	56,396,000	90,220,000	57,197,000
Total number of states general obligation bonds are held	36
Maximum portfolio concentration in municipal securities per corporate investment policy	20.00%
Revenue bonds, number owned by corporation	1
Revenue bond, fair value	500,000
Revenue bond, amortized cost	500,000
Investment Securities
Other investment securities pledged	3,200,000,000	3,200,000,000	2,700,000,000
Amount of municipal securities with a combined individual state to total municipal outstanding equal to or less than, per corporate policy	25.00%
12 states
Schedule of Investments [Line Items]
General obligation bonds, aggregate fair value	10,000,000
Collateralized Loan Obligations
Schedule of Investments [Line Items]
Available-for-sale Securities, Gross Unrealized Loss at End of Period	4,252,000	4,332,000	1,821,000
Available-for-sale	293,965,000	293,687,000	158,095,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss at End of Period	$ 4,252,000	$ 4,332,000	$ 1,821,000