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Income Taxes - Additional Information (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Tax Disclosure [Line Items]          
Tax cuts and jobs act, incomplete accounting, estimated income tax expense $ 11,900,000        
Tax cuts and jobs act, incomplete accounting, estimated write-down of deferred tax assets 9,200,000        
Tax cuts and jobs act, incomplete accounting, change in tax rate estimate income tax expense related to unrepatriated foreign earnings 2,700,000        
Deferred tax benefit recorded as an adjustment to other comprehensive income   $ 1,700,000 $ 1,500,000    
Foreign and domestic carry-forwards, unamortized research and development cost and state credit carry-forwards 10,000,000 10,000,000      
Net change in valuation allowance   (100,000)      
Cash and cash equivalents 86,433,000 86,433,000 79,895,000 $ 84,550,000 $ 73,439,000
Short-term investments 16,129,000 16,129,000 43,188,000    
Short-term liquidity amount 102,600,000 102,600,000 123,100,000    
Income tax benefit (expense) from stock options exercised adjustment to equity   0 0 (40,000)  
Unrecognized tax benefits 2,366,000 2,366,000 2,226,000 2,537,000 $ 3,334,000
Unrecognized tax benefits, effective tax rate 2,200,000 2,200,000 1,700,000 1,800,000  
Accrued interest and penalties 800,000 800,000 800,000 $ 900,000  
Foreign Subsidiaries [Member]          
Income Tax Disclosure [Line Items]          
Short-term liquidity amount $ 56,800,000 $ 56,800,000 $ 42,100,000    
Short-term liquidity, in percentage 55.40% 55.40% 34.20%    
Minimum [Member]          
Income Tax Disclosure [Line Items]          
Operating loss carry forwards expiration year   2018      
Maximum [Member]          
Income Tax Disclosure [Line Items]          
Operating loss carry forwards expiration year   2030