Intangible Assets - Intangible Assets Subject To Amortization (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	10 years 1 month 3 days
Gross Carrying Amount	$ 166,889	$ 208,270
Accumulated Amortization	$ 90,758	104,659
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	$ 19,837	19,020
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	$ 52,261	49,925
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	$ 5,858	5,732
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	$ 12,802	12,245
Renewal revenue
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	7 years 10 months 24 days
Gross Carrying Amount	$ 0	41,381
Accumulated Amortization	$ 0	$ 17,737