Loans and Allowance for Loan Losses - Summary of Loan Portfolio by Risk Rating (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Credit Risk Profile by Internally Assigned Rating
Total Loans	$ 1,438,219	$ 1,356,778
Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	1,404,089	1,320,970
Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	17,992	23,970
Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	16,138	11,838
Residential 1-4 Family [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	355,924	350,758
Residential 1-4 Family [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	346,779	339,529
Residential 1-4 Family [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	5,538	7,681
Residential 1-4 Family [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	3,607	3,548
Multifamily [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	50,559	31,242
Multifamily [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	50,559	31,242
Commercial Real Estate [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	585,217	564,965
Commercial Real Estate [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	562,510	545,301
Commercial Real Estate [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	11,603	13,313
Commercial Real Estate [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	11,104	6,351
Construction [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	277,518	245,830
Construction [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	277,150	243,416
Construction [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	320	2,362
Construction [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	48	52
Farmland [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	31,479	30,236
Farmland [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	30,451	29,260
Farmland [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	33	57
Farmland [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	995	919
Second Mortgages [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8,681	9,026
Second Mortgages [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8,089	8,007
Second Mortgages [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	296	347
Second Mortgages [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	296	672
Equity Lines of Credit [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	45,818	41,496
Equity Lines of Credit [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	45,637	41,274
Equity Lines of Credit [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	181	176
Equity Lines of Credit [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans		46
Commercial [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	29,532	30,000
Commercial [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	29,516	29,893
Commercial [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	13	18
Commercial [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	3	89
Agricultural [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	1,451	1,670
Agricultural [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	1,451	1,661
Agricultural [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans		2
Agricultural [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans		7
Installment and Other [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	52,040	51,555
Installment and Other [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	51,947	51,387
Installment and Other [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8	14
Installment and Other [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	$ 85	$ 154