FAIR VALUE MEASUREMENTS - Contingent consideration (Details) - Level 3 $ in Thousands	Jun. 30, 2019 USD ($) item	Dec. 31, 2018 USD ($) item
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration | $	$ 131,433	$ 98,905
Valuation techniques	us-gaap:ValuationTechniqueOptionPricingModelMember	us-gaap:ValuationTechniqueOptionPricingModelMember
Unobservable input	focs:MeasurementInputForecastedGrowthRatesMember	focs:MeasurementInputForecastedGrowthRatesMember
Minimum
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration (in percent)	(17.0)	(16.2)
Maximum
Inputs used in the fair value measurement of estimated contingent consideration
Estimated contingent consideration (in percent)	129.8	18.7