Equity Incentive Plan - Summary of Company's Restricted Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Sep. 11, 2017	May 16, 2017	Mar. 31, 2018
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted			24,182
Expected future remaining compensation expense			$ 280
Expected future compensation expense, restricted shares remaining vesting period			2 years 2 months 12 days
Restricted Shares Awarded on January 15, 2016 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted			6,160
Date of Award			Jan. 15, 2016
Expected future remaining compensation expense			$ 60
Expected future compensation expense, restricted shares remaining vesting period			2 years 9 months
Restricted Shares Awarded on March 11, 2016 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted			5,256
Date of Award			Mar. 11, 2016
Expected future remaining compensation expense			$ 25
Expected future compensation expense, restricted shares remaining vesting period			9 months
Restricted Shares Awarded on March 20, 2017 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted			7,814
Date of Award			Mar. 20, 2017
Expected future remaining compensation expense			$ 95
Expected future compensation expense, restricted shares remaining vesting period			1 year 9 months
Restricted Shares Awarded on March 20, 2017 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted			4,952
Date of Award			Mar. 20, 2017
Expected future remaining compensation expense			$ 100
Expected future compensation expense, restricted shares remaining vesting period			3 years 9 months
Restricted Stock [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Nonvested at beginning of period			42,138
Number of Restricted Shares, Granted	367	6,804
Number of Restricted Shares, Vested			(17,956)
Number of Restricted Shares, Forfeited			0
Number of Restricted Shares, Nonvested at end of period			24,182
Weighted Average Grant Date Fair Value, Nonvested at beginning of period			$ 15.60
Weighted Average Grant Date Fair Value, Vested			14.01
Weighted Average Grant Date Fair Value, Forfeited			0
Weighted Average Grant Date Fair Value, Nonvested at end of period			$ 16.78