Quarterly report pursuant to Section 13 or 15(d)

Intangible Assets (Intangible Assets Subject To Amortization) (Detail)

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Intangible Assets (Intangible Assets Subject To Amortization) (Detail) - USD ($)
$ in Thousands
 9 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 9 years 9 months 28 days  
Gross Carrying Amount $ 210,601 $ 174,259
Accumulated Amortization $ 66,704 51,258
Technology    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 7 years 10 months 24 days  
Gross Carrying Amount $ 25,563 23,483
Accumulated Amortization $ 11,672 9,223
Relationships With Financial Advisors    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 15 years 2 months 12 days  
Gross Carrying Amount $ 110,671 81,438
Accumulated Amortization $ 29,920 23,704
Vendor Relationship    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 7 years  
Gross Carrying Amount $ 3,613 3,613
Accumulated Amortization $ 3,613 3,458
Covenants Not-to-Compete    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 3 years 10 months 24 days  
Gross Carrying Amount $ 6,035 5,401
Accumulated Amortization $ 3,026 2,100
Customer Account    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 8 years 3 months 18 days  
Gross Carrying Amount $ 2,029 2,029
Accumulated Amortization $ 1,703 1,516
Renewal revenue    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 7 years 8 months 12 days  
Gross Carrying Amount $ 42,142 39,503
Accumulated Amortization $ 5,927 2,099
Trade names    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 7 years 10 months 24 days  
Gross Carrying Amount $ 16,910 15,154
Accumulated Amortization $ 7,233 5,563
Relationships With Investment Banking Clients    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 4 years  
Gross Carrying Amount $ 2,586 2,586
Accumulated Amortization $ 2,586 2,586
Leases    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 6 years  
Gross Carrying Amount $ 861 861
Accumulated Amortization $ 861 861
Referral Agreement    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 6 years 7 months 6 days  
Gross Carrying Amount $ 124 124
Accumulated Amortization $ 96 81
Other    
Indefinite-lived Intangible Assets [Line Items]    
Estimated useful life 6 years  
Gross Carrying Amount $ 67 67
Accumulated Amortization $ 67 $ 67