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Investments - Additional Information (Detail)
€ in Millions, $ in Millions
12 Months Ended
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Apr. 09, 2013
USD ($)
Apr. 09, 2013
EUR (€)
Investment [Line Items]          
Realized gain on trading securities $ 0.4 $ 8.2 $ 1.0    
Interest acquired in limited partnership   5.0      
Percentage of noncontrolling equity interest acquired 50.00%        
Maximum [Member]          
Investment [Line Items]          
Future capital commitment   $ 4.9      
Kleinwort Benson Investors International, Ltd. [Member]          
Investment [Line Items]          
Percentage of noncontrolling equity interest acquired       24.00% 24.00%
Noncontrolling equity interest acquired, amount       $ 3.4 € 2.6