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Allowance for Doubtful Accounts Included in Accounts Receivable Net (Detail) - USD ($)
$ in Millions
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Valuation Allowance [Line Items]      
Allowance for Doubtful Accounts $ 1.7 $ 1.3 $ 1.6