REVENUE - Deferred Revenue (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|
Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
Jun. 30, 2019 |
Dec. 31, 2018 |
Jun. 30, 2018 |
Dec. 31, 2017 |
|
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | ||||||||
| Deferred revenue | $ 45,263 | $ 33,614 | $ 45,263 | $ 33,614 | $ 44,812 | $ 36,451 | $ 27,155 | $ 1,590 |
| Deferred revenue arising from business combination | 0 | 22,800 | 0 | 22,800 | ||||
| Revenue recognized in the period from amounts included in deferred revenue at the beginning of the period | $ 12,656 | $ 10,165 | $ 28,280 | $ 1,539 | ||||
| Balances without adoption of ASC 606 | ||||||||
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | ||||||||
| Deferred revenue | 44,812 | 36,451 | 27,155 | 5,893 | ||||
| Accounting Standards Update 2014-09 | Effect of change | ||||||||
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | ||||||||
| Deferred revenue | $ 0 | $ 0 | $ 0 | $ (4,303) | ||||