FAIR VALUE MEASUREMENTS - Unobservable Inputs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value Measurements Using Unobservable Inputs (Level 3)
Contingent consideration attributable to and assumed from ABILITY Acquisition	$ (115)	$ (7,212)	$ 5,200
Level 3
Fair Value Measurements Using Unobservable Inputs (Level 3)
Balance, beginning of period	(31,824)	(7,400)
Fair value adjustment	532	(6,159)
Accretion expense (recognized in general and administrative expenses)	(647)	(1,053)
Settlement (payment) of liability	15,149	0
Balance, end of period	(16,790)	(31,824)	$ (7,400)
Level 3 | Goodwill
Fair Value Measurements Using Unobservable Inputs (Level 3)
Fair value adjustment	(300)	600
Level 3 | General and administrative
Fair Value Measurements Using Unobservable Inputs (Level 3)
Fair value adjustment	800	5,600
Level 3 | Contingent Consideration Attributable to Acquisition
Fair Value Measurements Using Unobservable Inputs (Level 3)
Contingent consideration attributable to and assumed from ABILITY Acquisition	$ 0	$ (17,212)