COMMITMENTS AND CONTINGENCIES - Lease cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
COMMITMENTS AND CONTINGENCIES
Operating leases	$ 1,165	$ 1,157	$ 2,347	$ 2,226
Variable lease costs (including insignificant short-term leases)	215	233	426	505
Sublease income as primary obligor	(249)	(247)	(495)	(493)
Total lease costs	$ 1,131	$ 1,143	$ 2,278	$ 2,238