Short-Term Investments - Additional Information (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Short-term investments	$ 42,057,000	$ 0

Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
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Name:	us-gaap_ShortTermInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant