Fair Value of Instruments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	$ 192,859	$ 196,398
U.S. Treasury [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	20,839	20,978
U.S. Government Agencies [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	79,493	80,466
Mortgage-backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	36,862	39,510
State and Local Governments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	55,665	55,444
Level 1 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	20,839	20,978
Level 1 [Member] \| Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	20,839	20,978
Level 1 [Member] \| U.S. Treasury [Member] \| Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	20,839	20,978
Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	170,597	173,992
Level 2 [Member] \| Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	170,597	173,992
Level 2 [Member] \| U.S. Government Agencies [Member] \| Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	79,493	80,466
Level 2 [Member] \| Mortgage-backed Securities [Member] \| Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	36,862	39,510
Level 2 [Member] \| State and Local Governments [Member] \| Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	54,242	54,016
Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	1,423	1,428
Level 3 [Member] \| Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	1,423	1,428
Level 3 [Member] \| State and Local Governments [Member] \| Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	$ 1,423	$ 1,428