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
Jun. 30, 2017
Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Marketable securities $ 29,498 $ 21,033
Fair Value Measurements Recurring    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 144,247 113,914
Gross unrealized losses (38) (30)
Fair value 144,209 113,884
Cash and cash equivalents 114,711 92,851
Marketable securities 29,498 21,033
Fair Value Measurements Recurring | Cash    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 58,032 48,533
Fair value 58,032 48,533
Cash and cash equivalents 58,032 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 52,239 39,277
Fair value 52,239 39,277
Cash and cash equivalents 52,239 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 15,912 15,904
Gross unrealized losses (15) (8)
Fair value 15,897 15,896
Cash and cash equivalents 3,438 5,041
Marketable securities 12,459 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 13,049 10,200
Gross unrealized losses (18) (22)
Fair value 13,031 10,178
Marketable securities 13,031 $ 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 5,015  
Gross unrealized losses (5)  
Fair value 5,010  
Cash and cash equivalents 1,002  
Marketable securities $ 4,008