Net loss per share attributable to common stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Numerator: | |||||||||||
| Net loss attributable to common stockholders, basic and diluted | $ (1,019) | $ (3,450) | $ (8,017) | $ (6,880) | $ (4,372) | $ (5,709) | $ (7,266) | $ (9,984) | $ (19,366) | $ (27,331) | $ (22,292) |
| Denominator: | |||||||||||
| Weighted average number of common stock, basic and diluted (in shares) | 39,824 | 38,025 | 36,849 | ||||||||
| Net loss per share attributable to common stockholders: | |||||||||||
| Basic and diluted (in dollars per share) | $ (0.02) | $ (0.09) | $ (0.20) | $ (0.18) | $ (0.11) | $ (0.15) | $ (0.19) | $ (0.27) | $ (0.49) | $ (0.72) | $ (0.60) |