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Financial Instruments - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value $ 153,802 $ 149,942
Liabilities fair value 1,368  
Money Market Funds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 109,265 104,544
Certificate of Deposit [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 7,000 7,814
Corporate Bonds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 15,234 17,701
Commercial Paper [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 9,965 7,476
U.S. Treasury Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 12,338 12,407
Earn-out Liability [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Liabilities fair value 1,368  
Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 116,265 112,358
Level 1 [Member] | Money Market Funds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 109,265 104,544
Level 1 [Member] | Certificate of Deposit [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 7,000 7,814
Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 37,537 37,584
Level 2 [Member] | Corporate Bonds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 15,234 17,701
Level 2 [Member] | Commercial Paper [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 9,965 7,476
Level 2 [Member] | U.S. Treasury Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 12,338 $ 12,407
Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Liabilities fair value 1,368  
Level 3 [Member] | Earn-out Liability [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Liabilities fair value $ 1,368