XML 52 R29.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Summary of Significant Accounting Policies - Summary of Fair Value Measurement Financial Asset and Liabilities (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Assets [Abstract] |  |
Cash and cash equivalents | $ 62,500 | $ 50,800
Total assets measured at fair value | 155,910 | 251,666
Money market funds |  |
Assets [Abstract] |  |
Cash and cash equivalents | 61,512 | 46,781
U.S Treasury securities |  |
Assets [Abstract] |  |
Marketable securities | 3,990 | 8,826
Government-sponsored enterprises |  |
Assets [Abstract] |  |
Marketable securities | 11,990 | 29,759
Corporate debt securities |  |
Assets [Abstract] |  |
Marketable securities | 78,418 | 166,300
Quoted Prices in Active Markets for Identical Assets, Level 1 |  |
Assets [Abstract] |  |
Total assets measured at fair value | 61,512 | 46,781
Quoted Prices in Active Markets for Identical Assets, Level 1 | Money market funds |  |
Assets [Abstract] |  |
Cash and cash equivalents | 61,512 | 46,781
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 | 94,398 | 204,885
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 | 3,990 | 8,826
Significant Other Observable Inputs, Level 2 | Government-sponsored enterprises |  |
Assets [Abstract] |  |
Marketable securities | 11,990 | 29,759
Significant Other Observable Inputs, Level 2 | Corporate debt securities |  |
Assets [Abstract] |  |
Marketable securities | 78,418 | 166,300
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

X
- 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=66048111&loc=d3e19207-110258 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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=75030427&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=82897076&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=82896770&loc=d3e26610-111562 + Details
Name: | us-gaap_AvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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 No definition available. + Details
Name: | us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |