ORGANIZATION AND SIGINIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 214,363,000	$ 73,475,000
Restricted cash	32,349,000	20,950,000
Total cash, cash equivalents and restricted cash	$ 246,712,000	$ 94,425,000	$ 69,959,000