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Revenue Recognition - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Disaggregation of Revenue [Line Items]      
Deferred revenue $ 1,419,000   $ 5,015,000
Customer payment period 0 years    
Deferred revenue current $ 2,769,000   5,791,000
Increase in revenue (18,000) $ (18,000)  
Accounting Standards Update 2014-09 [Member]      
Disaggregation of Revenue [Line Items]      
Deferred revenue 3,596,000    
Deferred revenue current 205,000    
Accounting Standards Update 2014-09 [Member] | Balances without adoption of Topic 606 [Member]      
Disaggregation of Revenue [Line Items]      
Deferred revenue     4,659,000
Gross deferred cost of revenue     $ 2,135,000
Deferred revenue current 6,842,000    
Accounting Standards Update 2014-09 [Member] | Adjustments [Member]      
Disaggregation of Revenue [Line Items]      
Deferred revenue current 4,073,000    
Increase in revenue $ 6,498,000    
Minimum [Member]      
Disaggregation of Revenue [Line Items]      
Recognition period 6 months    
Customer payment period 30 days    
Maximum [Member]      
Disaggregation of Revenue [Line Items]      
Recognition period 12 months    
Customer payment period 60 days