Loans and Allowance for Loan Losses - Summary of Loan Portfolio by Risk Rating (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Credit Risk Profile by Internally Assigned Rating
Total Loans	$ 1,745,295	$ 1,696,425
Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	1,729,552	1,680,267
Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	7,173	6,881
Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8,570	9,277
Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Residential 1-4 Family [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	409,497	393,268
Residential 1-4 Family [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	400,517	384,383
Residential 1-4 Family [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	5,801	5,616
Residential 1-4 Family [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	3,179	3,269
Residential 1-4 Family [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Multifamily [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	108,465	109,410
Multifamily [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	108,465	109,410
Multifamily [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Multifamily [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Multifamily [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Commercial Real Estate [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	695,865	689,695
Commercial Real Estate [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	690,966	684,202
Commercial Real Estate [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	754	668
Commercial Real Estate [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	4,145	4,825
Commercial Real Estate [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Construction [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	326,867	297,315
Construction [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	326,581	297,089
Construction [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	89	121
Construction [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	197	105
Construction [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Farmland [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	44,378	46,314
Farmland [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	43,529	45,470
Farmland [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	156	147
Farmland [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	693	697
Farmland [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Second mortgages [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8,859	9,193
Second mortgages [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8,449	8,775
Second mortgages [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	298	303
Second mortgages [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	112	115
Second mortgages [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Equity Lines of Credit [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	56,966	56,038
Equity Lines of Credit [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	56,788	55,883
Equity Lines of Credit [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	24	0
Equity Lines of Credit [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	154	155
Equity Lines of Credit [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Commercial [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	41,432	40,301
Commercial [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	41,429	40,301
Commercial [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	3	0
Commercial [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Commercial [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Agricultural, Installment and Other [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	52,966	54,891
Agricultural, Installment and Other [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	52,828	54,754
Agricultural, Installment and Other [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	48	26
Agricultural, Installment and Other [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	90	111
Agricultural, Installment and Other [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	$ 0	$ 0