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Revenue Recognition - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Mar. 31, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Jan. 01, 2017
Summary Of Accounting Policies [Line Items]            
Revenue $ 19,653,000   $ 22,467,000 $ 61,342,000 $ 70,644,000  
Topic 606 [Member]            
Summary Of Accounting Policies [Line Items]            
Cumulative-effect adjustment to retained earnings           $ 404,000
Asset impairment charges related to contract assets       0    
Capitalized contract acquisition costs 0     0   $ 292,000
Capitalized contract cost, amortization 12,000     160,000    
Impairment loss in relation to costs capitalized 0     0    
Topic 606 [Member] | Impact of changes in accounting policies, Effect of Change Higher/(Lower) [Member]            
Summary Of Accounting Policies [Line Items]            
Revenue $ (342,000) $ 2,800,000   $ 2,065,000