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Goodwill and Other Intangible Assets, Net - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Goodwill And Intangible Assets [Line Items]          
Goodwill recognized     $ 38,439,000   $ 91,300,000
Intangible amortization expense $ 7,300,000 $ 8,000,000 23,600,000 $ 23,000,000  
Impairment charges of indefinite life intangibles $ 0 $ 6,300,000 0 $ 6,300,000  
Real Estate Services [Member]          
Goodwill And Intangible Assets [Line Items]          
Goodwill recognized     $ 38,439,000