Investments and Fair Value of Financial Instruments - Summary of Fair Value of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets at Fair Value
Total Assets at Fair Value	$ 15,398	$ 52,594
Money Market Funds [Member]
Assets at Fair Value
Cash equivalents	2,631	1,549
Certificates of Deposit [Member]
Assets at Fair Value
Short-term investments	980	3,047
Commercial Paper [Member]
Assets at Fair Value
Short-term investments	4,290	21,248
U.S. Government Securities [Member]
Assets at Fair Value
Short-term investments	4,997	19,258
Long-term investments		2,498
Level 1 [Member]
Assets at Fair Value
Total Assets at Fair Value	7,628	23,305
Level 1 [Member] \| Money Market Funds [Member]
Assets at Fair Value
Cash equivalents	2,631	1,549
Level 1 [Member] \| Certificates of Deposit [Member]
Assets at Fair Value
Short-term investments	0	0
Level 1 [Member] \| Commercial Paper [Member]
Assets at Fair Value
Short-term investments	0	0
Level 1 [Member] \| U.S. Government Securities [Member]
Assets at Fair Value
Short-term investments	4,997	19,258
Long-term investments		2,498
Level 2 [Member]
Assets at Fair Value
Total Assets at Fair Value	7,770	29,289
Level 2 [Member] \| Money Market Funds [Member]
Assets at Fair Value
Cash equivalents	0	0
Level 2 [Member] \| Certificates of Deposit [Member]
Assets at Fair Value
Short-term investments	980	3,047
Level 2 [Member] \| Commercial Paper [Member]
Assets at Fair Value
Short-term investments	4,290	21,248
Level 2 [Member] \| U.S. Government Securities [Member]
Assets at Fair Value
Short-term investments	0	0
Long-term investments		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] \| Certificates of Deposit [Member]
Assets at Fair Value
Short-term investments	0	0
Level 3 [Member] \| Commercial Paper [Member]
Assets at Fair Value
Short-term investments	0	0
Level 3 [Member] \| U.S. Government Securities [Member]
Assets at Fair Value
Short-term investments	0	0
Long-term investments		0
U.S. Government Agency Securities [Member]
Assets at Fair Value
Short-term investments	2,500	4,994
U.S. Government Agency Securities [Member] \| Level 1 [Member]
Assets at Fair Value
Short-term investments	0	0
U.S. Government Agency Securities [Member] \| Level 2 [Member]
Assets at Fair Value
Short-term investments	2,500	4,994
U.S. Government Agency Securities [Member] \| Level 3 [Member]
Assets at Fair Value
Short-term investments	$ 0	$ 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

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Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&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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