Fair Value Measurement of Assets and Liabilities (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011
Available-for-sale debt securities	$ 863,196,000	$ 863,196,000
Foreclosed assets measured at fair value upon initial recognition	9,200,000	9,200,000
Charge-offs on initial recognition of foreclosed assets	1,200,000	2,300,000
Loss from a re-measurement of the repossessed asset at fair value	838,000	1,300,000
Impaired collateral dependent loans, charge-offs	4,300,000	4,600,000
Collateral dependent impaired loans, carrying value	60,000,000	60,000,000
Specific valuation allowance allocation	2,500,000	2,500,000
Collateral dependent impaired loans, fair value	57,500,000	57,500,000
Mortgage Backed Securities [Member]
Available-for-sale debt securities	44,800,000	44,800,000
Number of securities held	12	12
Corporate Bond [Member]
Available-for-sale debt securities	12,900,000	12,900,000
Number of securities held	4	4
Trading Securities [Member] | Trust Preferred Securities [Member]
Securities transferred from Level 3 to Level 2 during the period	21,900,000	21,900,000
Number of securities held	3	3
Pooled Trust Preferred Securities [Member] | Trust Preferred Securities [Member]
Number of securities held	1	1
Loan Servicing Rights [Member]
Impairment charges/net recoveries	49,000	101,000
Loan servicing rights, carrying value	11,700,000	11,700,000
Loan servicing rights, impaired	7,300,000	7,300,000
Loan servicing rights, valuation allowance	1,100,000	1,100,000
Trust Preferred Securities [Member]
Securities transferred from Level 3 to Level 2 during the period	$ 26,700,000	$ 26,700,000
Number of securities held	21	21