Fair Value of Instruments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	$ 244,786	$ 248,492
U.S. Treasury [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	38,904	25,393
U.S. Government Agency [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	100,804	119,234
Mortgage-backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	28,028	29,562
State and Local Governments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	77,050	74,303
Level 1 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	38,904	25,393
Level 1 [Member] | Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	38,904	25,393
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	38,904	25,393
Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	198,277	215,168
Level 2 [Member] | Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	198,277	215,168
Level 2 [Member] | U.S. Government Agency [Member] | Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	100,804	119,234
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	28,028	29,562
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	69,445	66,372
Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	7,605	7,931
Level 3 [Member] | Fair Value on a Recurring Basis [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	7,605	7,931
Level 3 [Member] | State and Local Governments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Securities Available for Sale	7,605	7,931	$ 7,907	$ 10,346
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	$ 7,605	$ 7,931