Stockholders' Equity - Additional Information (Detail) - USD ($)		9 Months Ended
	May 16, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule Of Stockholders Equity [Line Items]
Preferred stock, shares authorized		10,000,000		10,000,000
Preferred stock, par value		$ 0.001		$ 0.001
Preferred stock, shares issued		0		0
Preferred stock, shares outstanding		0		0
Common stock, shares authorized		200,000,000		200,000,000
Common stock, par value		$ 0.001		$ 0.001
Common stock, shares issued		15,313,383		15,302,455
Common stock, shares outstanding		15,313,383		15,302,455
Shares issued for Employee Stock Purchase Plan options, Value		$ 18,396
Employee stock purchase plan expense		$ 9,317	$ 14,686
Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Shares issued for Employee Stock Purchase Plan options, Shares		10,928
Shares issued for Employee Stock Purchase Plan options, Value		$ 11
2014 Employee Stock Purchase Plan [Member] | Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Shares issued for Employee Stock Purchase Plan options, Shares	10,928
Shares issued for Employee Stock Purchase Plan options, Value	$ 18,396