SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Contract assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Unbilled Receivables Current
Unbilled receivables, Balance at Beginning of Period	$ 3,279	$ 1,429
Unbilled receivables, Revenue Recognized In Advance of Billings	2,638	3,278
Unbilled receivables, Billings	(2,602)	(1,428)
Unbilled receivables, Balance at End of Period	$ 3,315	$ 3,279