SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING STANDARDS - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 89,785	$ 21,262	$ 24,353	$ 22,838
Restricted cash	0	0	0	130
Cash, cash equivalents and restricted cash	$ 89,785	$ 21,262	$ 24,353	$ 22,968