REVENUE - Net Revenue Earned by Category of Payer (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Net revenue	$ 804,713	$ 781,609	$ 740,848	$ 705,440	$ 720,779	$ 615,880	$ 497,266	$ 476,492	$ 3,032,610	$ 2,310,417	$ 1,939,791
Commercial payers
Disaggregation of Revenue [Line Items]
Net revenue									2,542,985	2,001,105	1,699,450
Government payers
Disaggregation of Revenue [Line Items]
Net revenue									450,067	285,128	217,876
Patients
Disaggregation of Revenue [Line Items]
Net revenue									$ 39,558	$ 24,184	$ 22,465