STOCKHOLDER EQUITY - Preferred stock summary (Details) - USD ($)
$ in Thousands |
Mar. 31, 2019 |
Dec. 31, 2018 |
Mar. 31, 2018 |
Dec. 31, 2017 |
| Preferred Stock |
|
|
|
|
| Preferred Stock Authorized |
10,883,950
|
10,883,950
|
|
|
| Preferred Stock Outstanding |
7,538,671
|
7,095,746
|
|
|
| Carrying Value |
$ 38,461
|
$ 35,410
|
|
|
| Liquidation Value |
$ 40,281
|
$ 36,964
|
|
|
| Common Stock Issuable Upon Conversion |
7,538,671
|
7,095,746
|
|
|
| Series A Convertible Preferred Stock |
|
|
|
|
| Preferred Stock |
|
|
|
|
| Preferred Stock Authorized |
3,093,898
|
3,093,898
|
|
|
| Preferred Stock Issued |
3,093,898
|
3,093,898
|
|
|
| Preferred Stock Outstanding |
3,093,898
|
3,093,898
|
3,093,898
|
3,093,898
|
| Carrying Value |
$ 6,254
|
$ 6,254
|
$ 6,254
|
$ 6,254
|
| Liquidation Value |
$ 7,000
|
$ 7,000
|
|
|
| Common Stock Issuable Upon Conversion |
3,093,898
|
3,093,898
|
|
|
| Series B Convertible Preferred Stock |
|
|
|
|
| Preferred Stock |
|
|
|
|
| Preferred Stock Authorized |
7,790,052
|
7,790,052
|
|
|
| Preferred Stock Issued |
4,444,773
|
4,001,848
|
|
|
| Preferred Stock Outstanding |
4,444,773
|
4,001,848
|
|
|
| Carrying Value |
$ 32,207
|
$ 29,156
|
|
|
| Liquidation Value |
$ 33,281
|
$ 29,964
|
|
|
| Common Stock Issuable Upon Conversion |
4,444,773
|
4,001,848
|
|
|