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Fair Value Measurement - Additional Information (Detail) - USD ($)
Dec. 31, 2018
Sep. 30, 2018
Dec. 31, 2017
Fair Value Measurement [Line Items]      
Restricted investments $ 19,200,000   $ 20,100,000
Estenson Logistics, LLC [Member]      
Fair Value Measurement [Line Items]      
Fair value of contingent consideration   $ 0