Fair Value Measurement - Carrying Amount and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Financial Assets:
Cash and due from financial institutions	$ 33,394	$ 36,695	$ 33,229	$ 35,561
Securities available for sale	229,419	195,864
Other securities	14,247	14,055
Loans, net of allowance for loan losses	1,129,046	1,042,201
Bank owned life insurance	24,981	24,552
Accrued interest receivable	4,999	3,854
Financial Liabilities:
Securities sold under agreement to repurchase	15,148	28,925
Carrying Amount [Member]
Financial Assets:
Cash and due from financial institutions	33,394	36,695
Securities available for sale	229,419	195,864
Other securities	14,247	14,055
Loans, held for sale	4,662	2,268
Loans, net of allowance for loan losses	1,129,046	1,042,201
Bank owned life insurance	24,981	24,552
Accrued interest receivable	4,999	3,854
Fair value swap asset	1,706	1,839
Financial Liabilities:
Nonmaturing deposits	947,262	913,677
Time deposits	254,027	207,426
Short-term FHLB advances	41,750	31,000
Long-term FHLB advances	15,000	17,500
Securities sold under agreement to repurchase	15,148	28,925
Subordinated debentures	29,427	29,427
Accrued interest payable	244	181
Swap liability	1,706	1,839
Total Fair Value [Member]
Financial Assets:
Cash and due from financial institutions	33,394	36,695
Securities available for sale	229,419	195,864
Other securities	14,247	14,055
Loans, held for sale	4,662	2,268
Loans, net of allowance for loan losses	1,130,083	1,047,329
Bank owned life insurance	24,981	24,552
Accrued interest receivable	4,999	3,854
Fair value swap asset	1,706	1,839
Financial Liabilities:
Nonmaturing deposits	947,262	913,677
Time deposits	254,017	207,784
Short-term FHLB advances	41,722	31,007
Long-term FHLB advances	14,966	17,553
Securities sold under agreement to repurchase	15,148	28,925
Subordinated debentures	29,470	27,414
Accrued interest payable	244	181
Swap liability	1,706	1,839
(Level 1) [Member]
Financial Assets:
Cash and due from financial institutions	33,394	36,695
Other securities	14,247	14,055
Loans, held for sale	4,662	2,268
Bank owned life insurance	24,981	24,552
Accrued interest receivable	4,999	3,854
Financial Liabilities:
Nonmaturing deposits	947,262	913,677
Short-term FHLB advances	41,722	31,007
Securities sold under agreement to repurchase	15,148	28,925
Accrued interest payable	244	181
(Level 2) [Member]
Financial Assets:
Securities available for sale	229,419	195,864
Fair value swap asset	1,706	1,839
Financial Liabilities:
Swap liability	1,706	1,839
(Level 3) [Member]
Financial Assets:
Loans, net of allowance for loan losses	1,130,083	1,047,329
Financial Liabilities:
Time deposits	254,017	207,784
Long-term FHLB advances	14,966	17,553
Subordinated debentures	$ 29,470	$ 27,414