REVENUE RECOGNITION AND ACCOUNTS RECEIVABLE - Summary of Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 51,231	$ 53,691
Medicaid
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	19,697	17,354
Medicare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	8,192	14,273
Managed Care
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	9,028	8,021
Private Pay and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 14,314	$ 14,043