STOCK-BASED COMPENSATION PLANS - Summary of stock option activity (Details) - Employee Stock Option [Member] $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Summary of stock option activity under the option Plan
Balance Beginning \| shares	1,885
Number of Shares, Granted \| shares	616
Number of Shares, Expired \| shares	(7)
Number of Shares, Forfeited \| shares	(115)
Number of Shares, Exercised \| shares	(253)
Balance Ending \| shares	2,126	1,885
Number of Shares, Exercisable \| shares	1,171
Weighted Average Exercise Price, Outstanding Beginning \| $ / shares	$ 0.80
Weighted Average Exercise Price, Granted \| $ / shares	5.62
Weighted Average Exercise Price, Expired \| $ / shares	1.00
Weighted Average Exercise Price, Exercised \| $ / shares	0.68
Weighted Average Exercise Price, Forfeited \| $ / shares	2.47
Weighted Average Exercise Price, Outstanding Ending \| $ / shares	2.12	$ 0.80
Weighted Average Exercise Price, Exercisable \| $ / shares	$ 0.43
Weighted Average Remaining Contractual Life, Outstanding	6 years 7 months 6 days	6 years 3 months 18 days
Weighted Average Remaining Contractual Life Exercisable	4 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding \| $	$ 15,720	$ 4,085
Aggregate Intrinsic Value, Exercisable \| $	$ 10,626

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Balance Type:	na
Period Type:	instant

- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.