Annual report pursuant to Section 13 and 15(d)

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

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Summary of Significant Accounting Policies - Summary of Fair Value Assets Measured on Recurring Basis for Cash, Cash Equivalents and Marketable Securities (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Marketable securities $ 21,033 $ 16,793
Fair Value Measurements Recurring    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 113,914 82,936
Gross unrealized losses (30) (37)
Fair value 113,884 82,899
Cash and cash equivalents 92,851 66,106
Marketable securities 21,033 16,793
Fair Value Measurements Recurring | Cash    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 48,533 52,164
Fair value 48,533 52,164
Cash and cash equivalents 48,533 52,164
Fair Value Measurements Recurring | Level 1 | Money Market Accounts    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 39,277 6,725
Fair value 39,277 6,725
Cash and cash equivalents 39,277 6,725
Fair Value Measurements Recurring | Level 2 | Certificates Of Deposit    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 15,904 24,047
Gross unrealized losses (8) (37)
Fair value 15,896 24,010
Cash and cash equivalents 5,041 7,217
Marketable securities 10,855 $ 16,793
Fair Value Measurements Recurring | Level 2 | Corporate Bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 10,200  
Gross unrealized losses (22)  
Fair value 10,178  
Marketable securities $ 10,178