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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, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Goodwill And Intangible Assets [Line Items]          
Additional goodwill recognized     $ 74,322,000   $ 37,100,000
Intangible amortization expense $ 8,000,000 $ 4,800,000 23,000,000 $ 15,000,000  
Impairment charges of definite and indefinite life intangibles $ 6,300 $ 0 6,300 $ 0  
Financial Services [Member]          
Goodwill And Intangible Assets [Line Items]          
Additional goodwill recognized     29,049,000    
Real Estate Services [Member]          
Goodwill And Intangible Assets [Line Items]          
Additional goodwill recognized     $ 45,273,000