LEASES - Components of lease expense (Details) - ASU No. 2016-02, Leases (Topic 842) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
LEASES
Total lease cost	$ 5,461	$ 17,275
Cost of revenues
LEASES
Operating lease cost	1,777	5,649
Short-term lease cost	932	3,325
Variable lease cost	2	3
Selling, general and administrative expenses
LEASES
Operating lease cost	1,839	5,845
Short-term lease cost	593	2,116
Variable lease cost	336	391
Sublease income	$ (18)	$ (54)