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Accounts Receivable - Summary of Accounts Receivable (Detail) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Contract receivables $ 62,787 $ 60,543
Allowance for doubtful accounts (2,883) (4,156)
Total accounts receivable 67,804 67,990
Trade Accounts Receivable [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Trade receivables $ 7,900 $ 11,603