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Fair Value of Financial Assets - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Investments $ 17,694 $ 10,060
Corporate Notes [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Investments 10,744 3,644
Commercial Paper [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Investments 6,950 6,416
Recurring [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Total assets 23,057 19,594
Recurring [Member] | Level 1 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Total assets 5,363 6,041
Recurring [Member] | Level 2 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Total assets 17,694 13,553
Recurring [Member] | Corporate Notes [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Investments 10,744 3,644
Recurring [Member] | Corporate Notes [Member] | Level 2 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Investments 10,744 3,644
Recurring [Member] | Commercial Paper [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Investments 6,950 6,416
Recurring [Member] | Commercial Paper [Member] | Level 2 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Investments 6,950 6,416
Recurring [Member] | Money Market Funds [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Cash equivalents 5,363 6,041
Recurring [Member] | Money Market Funds [Member] | Level 1 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Cash equivalents $ 5,363 6,041
Recurring [Member] | Corporate Notes [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Cash equivalents   998
Recurring [Member] | Corporate Notes [Member] | Level 2 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Cash equivalents   998
Recurring [Member] | Commercial Paper [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Cash equivalents   2,495
Recurring [Member] | Commercial Paper [Member] | Level 2 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Cash equivalents   $ 2,495