Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Financial Instruments - Summary of Fair Value Assets Measured on Recurring Basis for Cash, Cash Equivalents and Marketable Securities (Details)

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Fair Value of Financial Instruments - Summary of Fair Value Assets Measured on Recurring Basis for Cash, Cash Equivalents and Marketable Securities (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Marketable securities $ 33,395 $ 21,033
Fair Value Measurements Recurring    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 163,106 113,914
Gross unrealized losses (18) (30)
Fair value 163,088 113,884
Cash and cash equivalents 129,693 92,851
Marketable securities 33,395 21,033
Fair Value Measurements Recurring | Cash    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 50,670 48,533
Fair value 50,670 48,533
Cash and cash equivalents 50,670 48,533
Fair Value Measurements Recurring | Level 1 | Money Market Accounts    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 77,020 39,277
Fair value 77,020 39,277
Cash and cash equivalents 77,020 39,277
Fair Value Measurements Recurring | Level 2 | Certificates Of Deposit    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 14,302 15,904
Gross unrealized losses (3) (8)
Fair value 14,299 15,896
Cash and cash equivalents   5,041
Marketable securities 14,299 10,855
Fair Value Measurements Recurring | Level 2 | Corporate Bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 18,110 10,200
Gross unrealized losses (14) (22)
Fair value 18,096 10,178
Marketable securities 18,096 $ 10,178
Fair Value Measurements Recurring | Level 2 | Agency Mortgage-backed Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 3,004  
Gross unrealized losses (1)  
Fair value 3,003  
Cash and cash equivalents 2,003  
Marketable securities $ 1,000