Fair Value Measurements (Fair value hierarchy for its financial assets and liabilities) (Details) (USD $) In Thousands, unless otherwise specified
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Mar. 31, 2015
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Dec. 31, 2014
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Level 1 [Member] |
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Assets |
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Total cash equivalents and marketable securities |
$ 156,158us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
$ 20,354us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Level 1 [Member] | Money market funds [Member] |
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Assets |
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Total cash equivalents and marketable securities |
156,158us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
20,354us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Level 1 [Member] | U.S. agency debt securities [Member] |
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Assets |
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Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Level 1 [Member] | Government-backed security [Member] |
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Assets |
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Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Level 1 [Member] | Asset-backed securities [Member] |
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Assets |
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Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Level 1 [Member] | Corporate Debt Securities [Member] |
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Assets |
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Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Level 2 [Member] |
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Assets |
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Total cash equivalents and marketable securities |
166,406us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
143,221us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Level 2 [Member] | Money market funds [Member] |
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Assets |
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Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Level 2 [Member] | U.S. agency debt securities [Member] |
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Assets |
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Total cash equivalents and marketable securities |
35,721us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Level 2 [Member] | Government-backed security [Member] |
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Assets |
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Total cash equivalents and marketable securities |
18,000us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
7,500us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Level 2 [Member] | Asset-backed securities [Member] |
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Assets |
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Total cash equivalents and marketable securities |
46,639us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
46,624us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Level 2 [Member] | Corporate Debt Securities [Member] |
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Assets |
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Total cash equivalents and marketable securities |
66,046us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
89,097us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Level 3 [Member] |
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Assets |
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Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Level 3 [Member] | Money market funds [Member] |
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Assets |
|
|
Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Level 3 [Member] | U.S. agency debt securities [Member] |
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|
Assets |
|
|
Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Level 3 [Member] | Government-backed security [Member] |
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Assets |
|
|
Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Level 3 [Member] | Asset-backed securities [Member] |
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|
Assets |
|
|
Total cash equivalents and marketable securities |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Level 3 [Member] | Corporate Debt Securities [Member] |
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Assets |
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Total cash equivalents and marketable securities |
$ 0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
$ 0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |