Quarterly report pursuant to Section 13 or 15(d)

Intangible Assets - Intangible Assets Subject To Amortization (Details)

Intangible Assets - Intangible Assets Subject To Amortization (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	8 years 10 months 21 days
Gross Carrying Amount	$ 217,550	$ 217,550
Accumulated Amortization	$ 108,754	92,612
Technology
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	7 years 10 months 24 days
Gross Carrying Amount	$ 25,563	25,563
Accumulated Amortization	$ 18,204	15,754
Relationships with financial advisors
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	14 years 8 months 12 days
Gross Carrying Amount	$ 117,995	117,995
Accumulated Amortization	$ 47,590	40,505
Vendor relationships
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	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 (years)	3 years 10 months 24 days
Gross Carrying Amount	$ 6,421	6,421
Accumulated Amortization	$ 5,569	4,638
Customer accounts
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	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 (years)	7 years 8 months 12 days
Gross Carrying Amount	$ 16,910	16,910
Accumulated Amortization	$ 11,688	10,017
Renewal revenue
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	7 years 10 months 24 days
Gross Carrying Amount	$ 41,381	41,381
Accumulated Amortization	$ 16,423	12,481
Relationships with investment banking clients
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	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 (years)	6 years
Gross Carrying Amount	$ 861	861
Accumulated Amortization	$ 861	861
Referral agreement
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	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 (years)	6 years
Gross Carrying Amount	$ 67	67
Accumulated Amortization	$ 67	$ 67