Loans and Allowance for Loan Losses - Summary of Loan Portfolio by Risk Rating (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Credit Risk Profile by Internally Assigned Rating
Total Loans	$ 1,382,782	$ 1,356,778
Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	1,347,135	1,320,970
Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	19,959	23,970
Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	15,688	11,838
Residential 1-4 Family [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	352,539	350,758
Residential 1-4 Family [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	342,965	339,529
Residential 1-4 Family [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	5,941	7,681
Residential 1-4 Family [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	3,633	3,548
Multifamily [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	40,546	31,242
Multifamily [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	40,546	31,242
Commercial Real Estate [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	564,943	564,965
Commercial Real Estate [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	541,373	545,301
Commercial Real Estate [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	13,160	13,313
Commercial Real Estate [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	10,410	6,351
Construction [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	257,936	245,830
Construction [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	257,547	243,416
Construction [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	338	2,362
Construction [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	51	52
Farmland [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	30,879	30,236
Farmland [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	29,935	29,260
Farmland [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	34	57
Farmland [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	910	919
Second Mortgages [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8,868	9,026
Second Mortgages [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8,023	8,007
Second Mortgages [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	274	347
Second Mortgages [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	571	672
Equity Lines of Credit [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	43,728	41,496
Equity Lines of Credit [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	43,535	41,274
Equity Lines of Credit [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	187	176
Equity Lines of Credit [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	6	46
Commercial [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	30,357	30,000
Commercial [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	30,337	29,893
Commercial [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	17	18
Commercial [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	3	89
Agricultural, Installment and Other [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	52,986	53,225
Agricultural, Installment and Other [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	52,874	53,048
Agricultural, Installment and Other [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8	16
Agricultural, Installment and Other [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	$ 104	$ 161