Derivative Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative Financial Instruments Not Designated as Hedging Instruments
Asset Derivatives	$ 38,085	$ 30,891
Liability Derivatives	36,832	28,106
Net Gains (Losses) Recognized in the Statements of Income	12,785	19,510	18,955
Interest Rate Lock Commitments
Derivative Financial Instruments Not Designated as Hedging Instruments
Asset Derivatives	2,344	1,531
Liability Derivatives	10	1,648
Interest Rate Lock Commitments | Mortgage Banking
Derivative Financial Instruments Not Designated as Hedging Instruments
Net Gains (Losses) Recognized in the Statements of Income	14,091	15,007	13,221
Forward Commitments
Derivative Financial Instruments Not Designated as Hedging Instruments
Asset Derivatives	8	3,114
Liability Derivatives	946	155
Forward Commitments | Mortgage Banking
Derivative Financial Instruments Not Designated as Hedging Instruments
Net Gains (Losses) Recognized in the Statements of Income	(4,735)	1,227	1,746
Interest Rate Swap Agreements
Derivative Financial Instruments Not Designated as Hedging Instruments
Asset Derivatives	35,503	25,982
Liability Derivatives	35,779	26,197
Net liability positions with its financial institution counterparties	35,800
Collateral posted by the Company for net liability positions	3,600
Interest Rate Swap Agreements | Other Noninterest Income
Derivative Financial Instruments Not Designated as Hedging Instruments
Net Gains (Losses) Recognized in the Statements of Income	309	282	1,093
Foreign Exchange Contracts
Derivative Financial Instruments Not Designated as Hedging Instruments
Asset Derivatives	230	264
Liability Derivatives	97	106
Foreign Exchange Contracts | Other Noninterest Income
Derivative Financial Instruments Not Designated as Hedging Instruments
Net Gains (Losses) Recognized in the Statements of Income	$ 3,120	$ 2,994	$ 2,895