Annual report pursuant to Section 13 and 15(d)

Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Detail)

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Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Uncategorized [Abstract]                      
Revenue $ 3,764 $ 2,967 $ 408 $ 157 $ 2 $ 27 $ 196 $ 11 $ 7,296 $ 236 $ 508
Cost of goods sold (5,415) (3,528) (303) (34)         (9,280)    
Gross margin (1,651) (561) 105 123 2 27 196 11 (1,984) 236 508
Operating expenses (10,314) (10,132) (9,597) (7,646) (8,630) (7,726) (7,688) (4,307) (37,689) (28,351) (26,297)
Net loss $ (12,165) $ (10,669) $ (9,403) $ (7,375) $ (8,468) $ (7,483) $ (7,576) $ (4,370) $ (39,612) $ (27,897) $ (25,980)
Net loss per share $ (0.37) $ (0.32) $ (0.29) $ (0.23) $ (0.27) $ (0.23) $ (0.25) $ (0.16)