Loans and Allowance - Summary of Non-Accrual Loans by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 49,104	$ 56,402
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	7,139	9,283
Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	10,669	30
Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	951	4,978
Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	14,680	28,095
Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	13,546	12,068
Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,896	1,667
Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	223	117
Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans		$ 164