Fair Value - Carrying Amount and Estimated Fair Values of Financial Instrument (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 21,847	$ 56,829
Interest bearing deposits	4,995	5,245
Available-for-sale securities	102,391	130,810
Held-to-maturity securities	349,915	310,539
Loans held for sale	3,071	3,504
Loans, net of allowance for loan losses	949,990	954,849
Federal Reserve Bank and Federal Home Loan Bank stock	11,587	11,013
Interest receivable	4,712	4,540
Derivative Assets	1	2
Cash collateral held by derivative counterparty	157	24
Total assets	1,557,082	1,585,727
Deposits	1,177,732	1,215,914
Federal funds purchased and retail repurchase agreements	25,382	20,762
Federal Home Loan Bank advances	168,756	145,439
Bank stock loan		18,612
Subordinated debentures	9,431	9,251
Contractual obligations	2,831	3,093
Derivative Liabilities	1,003	246
Total liabilities	1,395,834	1,418,494
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	21,847	56,829
Interest bearing deposits	4,995	5,245
Available-for-sale securities	102,391	130,810
Held-to-maturity securities	349,915	310,539
Loans held for sale	3,071	3,504
Loans, net of allowance for loan losses	949,990	954,849
Federal Reserve Bank and Federal Home Loan Bank stock	11,587	11,013
Interest receivable	4,712	4,540
Derivative Assets		2
Cash collateral held by derivative counterparty	157	24
Total derivative assets	157	26
Total assets	1,448,665	1,477,355
Deposits	1,177,732	1,215,914
Federal funds purchased and retail repurchase agreements	25,382	20,762
Federal Home Loan Bank advances	168,756	145,439
Bank stock loan		18,612
Subordinated debentures	9,431	9,251
Contractual obligations	2,831	3,093
Interest payable	567	737
Derivative Liabilities	1,003	246
Cash collateral held by counterparty	(1,003)	(246)
Total liabilities	1,384,699	1,413,808
Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	21,847	56,829
Interest bearing deposits	4,995	5,245
Available-for-sale securities	102,391	130,810
Held-to-maturity securities	358,225	312,802
Loans held for sale	3,071	3,504
Loans, net of allowance for loan losses	946,120	957,039
Interest receivable	4,712	4,540
Derivative Assets		2
Cash collateral held by derivative counterparty	157
Cash collateral held by derivative counterparty		24
Total derivative assets	157	26
Total assets	1,441,518	1,470,795
Deposits	1,184,476	1,220,657
Federal funds purchased and retail repurchase agreements	25,382	20,762
Federal Home Loan Bank advances	168,756	145,439
Bank stock loan		18,612
Subordinated debentures	9,431	9,251
Contractual obligations	2,831	3,093
Interest payable	567	737
Derivative Liabilities	1,003	246
Cash collateral held by counterparty	(1,003)	(246)
Total liabilities	1,391,443	1,418,551
Estimated Fair Value [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	21,847	56,829
Available-for-sale securities	501
Cash collateral held by derivative counterparty	157
Cash collateral held by derivative counterparty		24
Total derivative assets	157	24
Total assets	22,505	56,853
Cash collateral held by counterparty	(1,003)	(246)
Total derivative liabilities	(1,003)	(246)
Total liabilities	(1,003)	(246)
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits	4,995	5,245
Available-for-sale securities	101,890	130,810
Held-to-maturity securities	358,225	312,802
Loans held for sale	3,071	3,504
Interest receivable	4,712	4,540
Derivative Assets		2
Total derivative assets		2
Total assets	472,893	456,903
Deposits	1,184,476	1,220,657
Federal funds purchased and retail repurchase agreements	25,382	20,762
Federal Home Loan Bank advances	168,756	145,439
Bank stock loan		18,612
Subordinated debentures	9,431	9,251
Contractual obligations	2,831	3,093
Interest payable	567	737
Derivative Liabilities	1,003	246
Total derivative liabilities	1,003	246
Total liabilities	1,392,446	1,418,797
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance for loan losses	946,120	957,039
Total assets	$ 946,120	$ 957,039