Quarterly financial data (unaudited) (Details) - USD ($) $ / shares in Units, $ 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 |
|
| Quarterly financial data (unaudited) | |||||||||||
| Revenue | $ 57,348 | $ 53,655 | $ 49,033 | $ 44,333 | $ 44,974 | $ 40,796 | $ 39,075 | $ 34,499 | $ 204,369 | $ 159,344 | $ 139,626 |
| Loss from operations | (3,464) | (2,989) | (7,670) | (6,578) | (4,074) | (5,387) | (6,969) | (9,667) | (20,701) | (26,097) | (21,631) |
| Net loss attributable to common stockholders | $ (1,019) | $ (3,450) | $ (8,017) | $ (6,880) | $ (4,372) | $ (5,709) | $ (7,266) | $ (9,984) | $ (19,366) | $ (27,331) | $ (22,292) |
| Basic and diluted loss per share (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) |