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Short-term investment	12 Months Ended
Short-term investment	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Short-term investment	Short-term investment As of December 31, 2017, the Company held a certificate of deposit of $4,500,000, with an original maturity at the date of purchase of one year. It is classified as Level 2 security in the fair value hierarchy.