ORGANIZATION AND SIGINIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 137,947,000	$ 214,363,000
Restricted cash	31,065,000	32,349,000
Total cash, cash equivalents and restricted cash	$ 169,012,000	$ 246,712,000	$ 219,661,000	$ 94,425,000