Commitments and Contingent Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Commitments to extend credit [Member]
Loan commitments and letters of credit
Financial instrument of credit risk	$ 1,480,490	$ 1,495,009
Financial standby letters of credit [Member]
Loan commitments and letters of credit
Financial instrument of credit risk	48,641	53,689
Performance standby letters of credit [Member]
Loan commitments and letters of credit
Financial instrument of credit risk	66,197	76,371
Commercial letters of credit [Member]
Loan commitments and letters of credit
Financial instrument of credit risk	$ 1,048	$ 1,297