Accounting Policies - Net Loss and Number of Shares Used to Calculate Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2015 |
Sep. 30, 2015 |
Jun. 30, 2015 |
Mar. 31, 2015 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Numerator: | |||||||||||
| Net loss and comprehensive loss | $ (15,337) | $ (16,422) | $ (22,082) | ||||||||
| Less: income from change in fair value of warrants | (332) | (2,141) | |||||||||
| Net loss attributable to common stockholders used to calculate diluted net loss per share | $ (15,337) | $ (16,754) | $ (24,223) | ||||||||
| Denominator: | |||||||||||
| Weighted-average shares outstanding - basic | 84,715,471 | 82,143,610 | 76,954,503 | ||||||||
| Potentially dilutive common shares outstanding: | |||||||||||
| Warrants | 707,000 | 1,586,000 | |||||||||
| Weighted-average shares used to calculate diluted net loss per share | 84,715,471 | 82,851,091 | 78,541,447 | ||||||||
| Basic - net loss per share | $ (0.08) | $ (0.07) | $ (0.08) | $ 0.06 | $ 0.04 | $ (0.08) | $ 0.01 | $ (0.16) | $ (0.18) | $ (0.20) | $ (0.29) |
| Dilutive - net loss per share | $ (0.10) | $ (0.07) | $ (0.08) | $ 0.06 | $ 0.04 | $ (0.08) | $ (0.05) | $ (0.16) | $ (0.18) | $ (0.20) | $ (0.31) |