BUSINESS COMBINATIONS - Restructuring charges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 1,577	$ 852	$ 5,953	$ 3,019
Costs to exit duplicative contracts [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	0	(478)	0	32
Workforce reduction [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	1,489	1,410	5,283	2,338
Other restructuring costs [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 88	$ (80)	$ 670	$ 649