ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES AND OTHER LIABILITIES - Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES AND OTHER LIABILITIES
Patient prepayments, deposits and refunds payable	$ 25,299		$ 30,194
Accrued professional fees	4,585		11,612
Insurance and self-insurance accruals	9,136		8,901
Accrued sales taxes and other taxes	6,800		6,335
Derivative liability	515
Accrued interest payable	501		845
Other current liabilities	7,954		8,421
Total accrued expenses and other current liabilities	$ 54,790	$ 67,335	$ 66,308