BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 23,329	$ 13,792	$ 24,422
Restricted cash	4,819	5,464	4,053
Total cash, cash equivalents and restricted cash	28,148	$ 19,256	$ 28,475	$ 286,226
Escrow Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 4,800