Loans and Allowance - Summary of Non-Accrual Loans by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 34,992	$ 53,399
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	6,467	12,195
Agriculture production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	31
Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	2,643	4,814
Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	16,187	22,612
Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	8,375	11,476
Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,093	1,997
Lease financing receivables, net of unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans		301
Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 164	$ 4