ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Credit card receivables	$ 2.0	$ 0.5
Cash and cash equivalents held in bank accounts in foreign countries	30.6	$ 27.5
South Korea
Cash and Cash Equivalents [Line Items]
Net assets	$ 32.7