ORGANIZATION AND SIGINIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 125,933,000	$ 108,282,000
Restricted cash	16,998,000	17,981,000
Total cash, cash equivalents and restricted cash	$ 142,931,000	$ 126,263,000	$ 164,005,000	$ 246,712,000