ACCRUED EXPENSES, OTHER CURRENT LIABILITIES AND OTHER LIABILITIES - Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
ACCRUED EXPENSES, OTHER CURRENT LIABILITIES AND OTHER LIABILITIES
Patient prepayments deposits and refunds payable	$ 28,895				$ 24,169
Accrued sales taxes and other taxes	5,716				5,888
Accrued professional fees	25,912				32,824
Insurance and self-insurance accruals	9,866				7,495
Other current liabilities	8,561				9,484
Total accrued expenses and other current liabilities	$ 78,950	$ 75,443	$ 78,026	$ 81,934	$ 79,860	$ 91,798	$ 91,117	$ 86,465