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Goodwill and Other Intangible Assets, Net - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Goodwill And Intangible Assets [Line Items]          
Goodwill recognized     $ 6,626,000   $ 91,300,000
Intangible amortization expense $ 7,600,000 $ 8,800,000 16,300,000 $ 15,000,000  
Impairment charges of indefinite life intangibles $ 0 $ 0 0 $ 0  
Real Estate Services [Member]          
Goodwill And Intangible Assets [Line Items]          
Goodwill recognized     $ 6,626,000