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Revenue Recognition and Accounts Receivable - Additional Information (Detail) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Jan. 01, 2018
Other Contract Assets [Member]      
Revenue Recognition And Accounts Receivable [Line Items]      
Other contract assets impairment $ 0 $ 0  
Other Noncurrent Assets [Member]      
Revenue Recognition And Accounts Receivable [Line Items]      
Other contract assets $ 1,100,000 $ 1,000,000.0  
Topic 606 [Member]      
Revenue Recognition And Accounts Receivable [Line Items]      
Net increase to opening retained earnings due to cumulative impact of adoption     $ 4,800,000