Intangible Assets - Intangible Assets Subject To Amortization (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	9 years 8 months 65 days
Gross Carrying Amount	$ 175,565	$ 175,565
Accumulated Amortization	$ 106,123	102,501
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	$ 22,944	22,187
Relationships with financial advisors
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	14 years 3 months 12 days
Gross Carrying Amount	$ 126,122	126,122
Accumulated Amortization	$ 62,200	59,584
Covenants not-to-compete
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	3 years 8 months 55 days
Gross Carrying Amount	$ 6,964	6,964
Accumulated Amortization	$ 6,378	6,258
Trade names
Indefinite-lived Intangible Assets [Line Items]
Weighted-Average Estimated Useful Life (years)	7 years 7 months 55 days
Gross Carrying Amount	$ 16,916	16,916
Accumulated Amortization	$ 14,601	$ 14,472