Investments and Fair Value Measurements - Summary of Fair Value of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets at Fair Value
Total Assets at Fair Value	$ 21,072	$ 12,841
Money Market Funds [Member]
Assets at Fair Value
Cash equivalents	9,902	8,943
Commercial Paper [Member]
Assets at Fair Value
Cash equivalents	1,345
Short-term investments	6,776	1,399
Treasury Bills [Member]
Assets at Fair Value
Short-term investments	1,195
U.S. Government Securities [Member]
Assets at Fair Value
Short-term investments	1,198	2,499
Level 1 [Member]
Assets at Fair Value
Total Assets at Fair Value	12,295	11,442
Level 1 [Member] \| Money Market Funds [Member]
Assets at Fair Value
Cash equivalents	9,902	8,943
Level 1 [Member] \| Commercial Paper [Member]
Assets at Fair Value
Cash equivalents	0
Short-term investments	0	0
Level 1 [Member] \| Treasury Bills [Member]
Assets at Fair Value
Short-term investments	1,195
Level 1 [Member] \| U.S. Government Securities [Member]
Assets at Fair Value
Short-term investments	1,198	2,499
Level 2 [Member]
Assets at Fair Value
Total Assets at Fair Value	8,777	1,399
Level 2 [Member] \| Money Market Funds [Member]
Assets at Fair Value
Cash equivalents	0	0
Level 2 [Member] \| Commercial Paper [Member]
Assets at Fair Value
Cash equivalents	1,345
Short-term investments	6,776	1,399
Level 2 [Member] \| Treasury Bills [Member]
Assets at Fair Value
Short-term investments	0
Level 2 [Member] \| U.S. Government Securities [Member]
Assets at Fair Value
Short-term investments	0	0
Level 3 [Member]
Assets at Fair Value
Total Assets at Fair Value	0	0
Level 3 [Member] \| Money Market Funds [Member]
Assets at Fair Value
Cash equivalents	0	0
Level 3 [Member] \| Commercial Paper [Member]
Assets at Fair Value
Cash equivalents	0
Short-term investments	0	0
Level 3 [Member] \| Treasury Bills [Member]
Assets at Fair Value
Short-term investments	0
Level 3 [Member] \| U.S. Government Securities [Member]
Assets at Fair Value
Short-term investments	0	$ 0
Corporate Securities [Member]
Assets at Fair Value
Short-term investments	656
Corporate Securities [Member] \| Level 1 [Member]
Assets at Fair Value
Short-term investments	0
Corporate Securities [Member] \| Level 2 [Member]
Assets at Fair Value
Short-term investments	656
Corporate Securities [Member] \| Level 3 [Member]
Assets at Fair Value
Short-term investments	$ 0

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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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562

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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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