FAIR VALUE MEASUREMENTS - Contingent consideration (Details) $ in Thousands	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Minimum | Discount Rates
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration (in percent)	6.5
Maximum | Discount Rates
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration (in percent)	18.0
Level 3
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration	$ 115,000	$ 183,568
Level 3 | Minimum | Forecasted growth rates
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration (in percent)	(26.3)	(10.7)
Level 3 | Minimum | Discount Rates
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration (in percent)		11.0
Level 3 | Maximum | Forecasted growth rates
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration (in percent)	57.5	51.1
Level 3 | Maximum | Discount Rates
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration (in percent)		17.0