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Summary of Significant Accounting Policies - Summary of Fair Value Measurement Financial Asset and Liabilities (Details) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Assets [Abstract] |  |
Cash and cash equivalents | $ 50,800 | $ 108,000
Total assets measured at fair value | 251,666 | 250,831
Money market funds |  |
Assets [Abstract] |  |
Cash and cash equivalents | 46,781 | 62,353
U.S Treasury securities |  |
Assets [Abstract] |  |
Marketable securities | 8,826 | 9,348
Government-sponsored enterprises |  |
Assets [Abstract] |  |
Marketable securities | 29,759 | 41,202
Corporate debt securities |  |
Assets [Abstract] |  |
Marketable securities | 166,300 | 137,928
Quoted Prices in Active Markets for Identical Assets, Level 1 |  |
Assets [Abstract] |  |
Total assets measured at fair value | 46,781 | 62,353
Quoted Prices in Active Markets for Identical Assets, Level 1 | Money market funds |  |
Assets [Abstract] |  |
Cash and cash equivalents | 46,781 | 62,353
Quoted Prices in Active Markets for Identical Assets, Level 1 | U.S Treasury securities |  |
Assets [Abstract] |  |
Marketable securities | 0 | 0
Quoted Prices in Active Markets for Identical Assets, Level 1 | Government-sponsored enterprises |  |
Assets [Abstract] |  |
Marketable securities | 0 | 0
Quoted Prices in Active Markets for Identical Assets, Level 1 | Corporate debt securities |  |
Assets [Abstract] |  |
Marketable securities | 0 | 0
Significant Other Observable Inputs, Level 2 |  |
Assets [Abstract] |  |
Total assets measured at fair value | 204,885 | 188,478
Significant Other Observable Inputs, Level 2 | Money market funds |  |
Assets [Abstract] |  |
Cash and cash equivalents | 0 | 0
Significant Other Observable Inputs, Level 2 | U.S Treasury securities |  |
Assets [Abstract] |  |
Marketable securities | 8,826 | 9,348
Significant Other Observable Inputs, Level 2 | Government-sponsored enterprises |  |
Assets [Abstract] |  |
Marketable securities | 29,759 | 41,202
Significant Other Observable Inputs, Level 2 | Corporate debt securities |  |
Assets [Abstract] |  |
Marketable securities | 166,300 | 137,928
Significant Unobservable Inputs, Level 3 |  |
Assets [Abstract] |  |
Total assets measured at fair value | 0 | 0
Significant Unobservable Inputs, Level 3 | Money market funds |  |
Assets [Abstract] |  |
Cash and cash equivalents | 0 | 0
Significant Unobservable Inputs, Level 3 | U.S Treasury securities |  |
Assets [Abstract] |  |
Marketable securities | 0 | 0
Significant Unobservable Inputs, Level 3 | Government-sponsored enterprises |  |
Assets [Abstract] |  |
Marketable securities | 0 | 0
Significant Unobservable Inputs, Level 3 | Corporate debt securities |  |
Assets [Abstract] |  |
Marketable securities | $ 0 | $ 0

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References 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=36462937&loc=d3e19207-110258 + Details
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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=51813488&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=27724398&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=49167202&loc=d3e26610-111562 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 + Details
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