Fair Value of Assets and Liabilities (Financial instruments not recorded at FV on recurring basis) (Details 6) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financial Instruments - Assets
Held-to-Maturity: Fair Value	$ 4,181,613	$ 4,504,495
Carrying Amount
Financial Instruments - Assets
Held-to-Maturity: Fair Value	4,121,768	4,466,679
Loans	7,354,296	6,542,719
Financial Instruments - Liabilities
Time Deposits	1,186,245	1,434,001
Securities Sold Under Agreements to Repurchase	632,138	688,601
Long-Term Debt	259,938	163,005
Fair Value
Financial Instruments - Assets
Held-to-Maturity: Fair Value	4,181,613	4,504,495
Loans	7,837,382	7,048,757
Financial Instruments - Liabilities
Time Deposits	1,190,119	1,437,064
Securities Sold Under Agreements to Repurchase	700,916	758,781
Long-Term Debt	262,061	163,911
Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments - Assets
Held-to-Maturity: Fair Value	504,344	499,616
Loans	0	0
Financial Instruments - Liabilities
Time Deposits	0	0
Securities Sold Under Agreements to Repurchase	0	0
Long-Term Debt	0	0
Fair Value | Significant Other Observable Inputs (Level 2)
Financial Instruments - Assets
Held-to-Maturity: Fair Value	3,677,269	4,004,879
Loans	0	0
Financial Instruments - Liabilities
Time Deposits	1,190,119	1,437,064
Securities Sold Under Agreements to Repurchase	700,916	758,781
Long-Term Debt	262,061	163,911
Fair Value | Significant Other Unobservable Inputs (Level 3)
Financial Instruments - Assets
Held-to-Maturity: Fair Value	0	0
Loans	7,837,382	7,048,757
Financial Instruments - Liabilities
Time Deposits	0	0
Securities Sold Under Agreements to Repurchase	0	0
Long-Term Debt	$ 0	$ 0