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Goodwill and Other Intangible Assets, Net - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2015
USD ($)
Business
Nov. 01, 2015
USD ($)
Dec. 31, 2014
USD ($)
Business
Dec. 31, 2013
USD ($)
Finite-Lived Intangible Assets [Line Items]        
Additions to goodwill     $ 51,900,000  
Decrease to goodwill resulting from business divestiture $ 1,554,000   1,537,000  
Goodwill 447,685,000   $ 435,231,000 $ 384,697,000
Goodwill, Impairment Loss $ 0 $ 0    
Finite-Lived Intangible Asset, Useful Life 7 years 9 months 18 days      
Minimum [Member]        
Finite-Lived Intangible Assets [Line Items]        
Finite-Lived Intangible Asset, Useful Life 2 years      
Maximum [Member]        
Finite-Lived Intangible Assets [Line Items]        
Finite-Lived Intangible Asset, Useful Life 15 years      
Client Lists [Member]        
Finite-Lived Intangible Assets [Line Items]        
Remaining weighted average amortization period remaining for total intangible assets 7 years 7 months 6 days      
Other Intangible Assets [Member]        
Finite-Lived Intangible Assets [Line Items]        
Finite-Lived Intangible Asset, Useful Life 10 years      
Other Intangible Assets [Member] | Minimum [Member]        
Finite-Lived Intangible Assets [Line Items]        
Finite-Lived Intangible Asset, Useful Life 2 years      
Other Intangible Assets [Member] | Maximum [Member]        
Finite-Lived Intangible Assets [Line Items]        
Finite-Lived Intangible Asset, Useful Life 15 years      
Financial Services Practice Group [Member]        
Finite-Lived Intangible Assets [Line Items]        
Number of businesses sold | Business 3   1  
Decrease to goodwill resulting from business divestiture $ 1,600,000   $ 1,500,000  
Employee Services [Member]        
Finite-Lived Intangible Assets [Line Items]        
Additions to goodwill 13,500,000   42,600,000  
Goodwill $ 178,534,000   164,935,000 122,316,000
Financial Services [Member]        
Finite-Lived Intangible Assets [Line Items]        
Additions to goodwill     9,300,000  
Number of businesses sold | Business 2      
Decrease to goodwill resulting from business divestiture $ 1,554,000   1,537,000  
Goodwill $ 267,485,000   $ 268,630,000 $ 260,715,000