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Fair Value of Financial Instruments (Details) - Recurring [Member]
$ in Thousands
Mar. 31, 2018
USD ($)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Fair value of financial instruments $ 91,471
Money Market Mutual Funds [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 79,910
Certificates of Deposit [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 1,546
United States Treasury Securities [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 10,015
Short-term Investments [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 11,561
Level 1 [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Fair value of financial instruments 91,471
Level 1 [Member] | Money Market Mutual Funds [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 79,910
Level 1 [Member] | Certificates of Deposit [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 1,546
Level 1 [Member] | United States Treasury Securities [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 10,015
Level 1 [Member] | Short-term Investments [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 11,561
Level 2 [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Fair value of financial instruments 0
Level 2 [Member] | Money Market Mutual Funds [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 0
Level 2 [Member] | Certificates of Deposit [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 0
Level 2 [Member] | United States Treasury Securities [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 0
Level 2 [Member] | Short-term Investments [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 0
Level 3 [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Fair value of financial instruments 0
Level 3 [Member] | Money Market Mutual Funds [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 0
Level 3 [Member] | Certificates of Deposit [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 0
Level 3 [Member] | United States Treasury Securities [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents 0
Level 3 [Member] | Short-term Investments [Member]  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]  
Cash and cash equivalents $ 0