Loans and Allowance - Summary of Non-Accrual Loans by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 38,971	$ 53,399
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	8,543	12,195
Agriculture production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	33
Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	2,492	4,814
Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	15,352	22,612
Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	11,148	11,476
Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,234	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	$ 169	$ 4