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Fair Value Measurement - Additional Information (Detail) - USD ($)
Sep. 30, 2018
Dec. 31, 2017
Fair Value Measurement [Line Items]    
Fair value of fixed-rate borrowings less than historical carrying value $ 3,600,000 $ 2,400,000
Fixed-rate borrowings, carrying value 303,500,000 247,100,000
Restricted investments 22,200,000 $ 20,100,000
Estenson Logistics, LLC [Member]    
Fair Value Measurement [Line Items]    
Fair value of contingent consideration $ 0