INCOME TAXES - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Gross unrecognized tax benefits, beginning of the period	$ 46,541	$ 45,154	$ 41,460
Increases in tax positions for prior years	2,789	1,377	3,655
Decreases in tax positions for prior years	0	(1,860)	0
Increases in tax positions for current year	11,784	5,516	8,090
Increases in tax positions acquired or assumed in a business combination	0	0	0
Decreases due to lapses of statutes of limitations	(5,642)	(3,646)	(8,051)
Gross unrecognized tax benefits, end of the period	$ 55,472	$ 46,541	$ 45,154