Fair Value Measurements (Details) - Recurring basis - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets
Total assets	$ 16,288	$ 19,047
U.S. Treasury securities
Assets
Investments	1,493	4,998
Money market funds
Assets
Cash and cash equivalents, fair value	13,807	14,049
Certificates of deposit
Assets
Investments	988
Level 1
Assets
Total assets	14,795	14,049
Level 1 \| Money market funds
Assets
Cash and cash equivalents, fair value	13,807	14,049
Level 1 \| Certificates of deposit
Assets
Investments	988
Level 2
Assets
Total assets	1,493	4,998
Level 2 \| U.S. Treasury securities
Assets
Investments	$ 1,493	$ 4,998

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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