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
Mar. 31, 2017
Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Marketable securities $ 23,135 $ 21,033
Fair Value Measurements Recurring    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 128,269 113,914
Gross unrealized losses (29) (30)
Fair value 128,240 113,884
Cash and cash equivalents 105,105 92,851
Marketable securities 23,135 21,033
Fair Value Measurements Recurring | Cash    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Adjusted cost 51,200 48,533
Fair value 51,200 48,533
Cash and cash equivalents 51,200 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 46,162 39,277
Fair value 46,162 39,277
Cash and cash equivalents 46,162 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 13,586 15,904
Gross unrealized losses (4) (8)
Fair value 13,582 15,896
Cash and cash equivalents 1,718 5,041
Marketable securities 11,864 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 13,316 10,200
Gross unrealized losses (21) (22)
Fair value 13,295 10,178
Cash and cash equivalents 6,025  
Marketable securities 7,270 $ 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 4,005  
Gross unrealized losses (4)  
Fair value 4,001  
Marketable securities $ 4,001