SIGNIFICANT ACCOUNTING POLICIES - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 25,452	$ 11,789
Funds held by lender and restricted cash	198	143
Total cash, cash equivalents, and restricted cash	$ 25,650	$ 11,932	$ 13,689