Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
Intangible Assets (Intangible Assets Subject To Amortization) (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 8 years 9 months 27 days  
Gross Carrying Amount $ 217,550 $ 217,550
Accumulated Amortization $ 113,939 92,612
Technology    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 7 years 9 months 60 days  
Gross Carrying Amount $ 25,563 25,563
Accumulated Amortization $ 19,020 15,754
Relationships with financial advisors    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 14 years 7 months 30 days  
Gross Carrying Amount $ 117,995 117,995
Accumulated Amortization $ 49,925 40,505
Vendor relationships    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 7 years  
Gross Carrying Amount $ 3,613 3,613
Accumulated Amortization $ 3,613 3,613
Covenants not-to-compete    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 3 years 10 months 24 days  
Gross Carrying Amount $ 6,421 6,421
Accumulated Amortization $ 5,732 4,638
Customer accounts    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 8 years 3 months 18 days  
Gross Carrying Amount $ 2,029 2,029
Accumulated Amortization $ 2,029 1,971
Trade names    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 7 years 8 months 12 days  
Gross Carrying Amount $ 16,910 16,910
Accumulated Amortization $ 12,245 10,017
Renewal revenue    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 7 years 10 months 24 days  
Gross Carrying Amount $ 41,381 41,381
Accumulated Amortization $ 17,737 12,481
Relationships with investment banking clients    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average 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]    
Weighted-Average Estimated Useful Life 6 years  
Gross Carrying Amount $ 861 861
Accumulated Amortization $ 861 861
Referral agreement    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 6 years 7 months 6 days  
Gross Carrying Amount $ 124 124
Accumulated Amortization $ 124 119
Other    
Indefinite-lived Intangible Assets [Line Items]    
Weighted-Average Estimated Useful Life 6 years  
Gross Carrying Amount $ 67 67
Accumulated Amortization $ 67 $ 67