Stockholders' Equity - Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	May 03, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	May 02, 2017
Sale Of Stock [Line Items]
Payroll withholdings from employees		$ 135,000	$ 99,000	$ 135,000	$ 99,000
Issuance of common stock under employee stock purchase plan				75,529	34,067
Stock options granted		0	0
Unrecognized compensation costs		$ 2,100,000		$ 2,100,000
Weighted average period				1 year 2 months 13 days
Amended and Restated ESPP [Member]
Sale Of Stock [Line Items]
Increase in number of shares of common stock reserved under the plan	100,000
Number of shares increased annually to common stock shares reserved for issuance	100,000					30,000
Aggregate number of shares of common stock reserved under the plan	1,250,000
Award plan expiration year	2027