ACCRUED EXPENSES, OTHER CURRENT LIABILITIES AND OTHER LIABILITIES - Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013
ACCRUED EXPENSES, OTHER CURRENT LIABILITIES AND OTHER LIABILITIES
Accrued professional fees	$ 38,522				$ 1,038
Other current liabilities	16,900				13,723
Accrued insurance	15,881				14,790
Patient prepayments deposits and refunds payable	9,263				8,644
Accrued sales taxes and other taxes	11,212				6,238
Total	$ 91,778	$ 68,118	$ 47,436	$ 44,508	$ 44,433	$ 41,043	$ 41,605	$ 40,096