DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues	$ 47,966	$ 51,337	$ 54,357	$ 52,887	$ 57,122	$ 50,703	$ 47,268	$ 46,483	$ 206,547	$ 201,576	$ 176,842
Performance obligations transferred at a point in time [Member]
Revenues									205,422	200,557	176,842
Performance obligations transferred over time [Member]
Revenues									$ 1,125	$ 1,019	$ 0