Loans and Allowance - Summary of Non-Accrual Loans by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 44,321	$ 48,789
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	8,249	7,048
Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,978	5,800
Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,585	1,439
Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	16,931	19,350
Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	13,314	12,933
Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	2,141	1,988
Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	123	231
Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans