SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Short-Term Investments (Details) - Certificates of Deposit	12 Months Ended
Dec. 31, 2017
Minimum
Short-term investments
Maturity period	1 month
Maximum
Short-term investments
Maturity period	12 months

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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