Loans - Additional Information (Detail) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 8,070,000	$ 10,569,000
Deferred loan origination costs	16,000,000	17,100,000
Total loans	5,634,957,000	5,632,716,000
1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	8,100,000	10,600,000
Total commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,471,781,000	2,415,932,000
Total commercial | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Analysis of loans individually by classification of credit risk	500,000.0
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	159,447,000	150,102,000
Other | Farm Land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	42,300,000	42,800,000
Other | State and Political Subdivision Obligations
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	103,300,000	96,200,000
Other | Deposit Customer Overdraft
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 1,300,000	$ 1,300,000