ORGANIZATION AND SIGINIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 108,282,000	$ 214,363,000
Restricted cash	17,981,000	32,349,000
Total cash, cash equivalents and restricted cash	$ 126,263,000	$ 246,712,000	$ 94,425,000	$ 69,959,000