Organization, basis of presentation and summary of significant policies - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Common Stock, par value	$ 0.001	$ 0.001
Inventory obsolescence reserved	$ 177	$ 243
Sales return maximum duration	18 months
Offered period for sales return prior to expiration	6 months
Offered period for sales return subsequent to expiration	12 months
Discount for prompt payment	2.00%