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Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2017
Dec. 31, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Highly liquid marketable securities with original maturities     90 days or less  
Cash equivalents include commercial paper and money market securities     $ 39,761,000 $ 10,881,000
Short-term marketable securities maturity description     Over 90 days that mature in less than one-year  
Marketable securities other-than temporary impairments     $ 0  
Credit exposure to any one financial institution or type of financial instrument     5% of its cash equivalents and marketable securities or $1,000, whichever is greater  
Percentage of credit exposure to any one financial institution or type of financial instrument     5.00%  
Maximum amount of credit exposure to any one financial institution or type of financial instrument     $ 1,000,000  
Credit exposure limits of cash and cash equivalents and marketable securities     40% of its cash equivalents and marketable securities, or $15,000, whichever is greater  
Percentage of credit exposure limits based on cash and cash equivalents and marketable securities     40.00%  
Credit exposure limits of cash and cash equivalents and marketable securities under option two     $ 15,000,000  
Purchase price adjustment date     1 year  
Impairment of goodwill $ 0 $ 0    
Term of patent     17 years  
ASU No. 2016-09 [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Unrecognized excess tax benefits of deferred tax assets offset by valuation allowance       $ 6,219,000
ASU No. 2016-09 [Member] | Retained Earnings [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Adjustment to opening retained earnings     $ 25,000