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Marketable Securities and Fair Value Measurements - Estimate of Fair Value of Marketable Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 83,991 | $ 85,417
Gross Unrealized Gains | 18 | 19
Gross Unrealized Losses | (36) | (64)
Fair Value | 83,973 | 85,372
Certificates of deposit |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 15,990 | 12,499
Gross Unrealized Gains | 4 | 9
Gross Unrealized Losses | (1) | 0
Fair Value | 15,993 | 12,508
Corporate securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 40,941 | 42,765
Gross Unrealized Gains | 12 | 9
Gross Unrealized Losses | (13) | (42)
Fair Value | 40,940 | 42,732
U.S. Treasury and agency securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 3,494 | 5,190
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (12) | (14)
Fair Value | 3,482 | 5,176
Commercial paper |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 9,214 | 11,470
Gross Unrealized Gains | 2 | 1
Gross Unrealized Losses | 0 | (2)
Fair Value | 9,216 | 11,469
Asset-backed securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 14,352 | 13,493
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (10) | (6)
Fair Value | $ 14,342 | $ 13,487

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + 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=65884222&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562 + Details
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