Segment Information and Revenues - Details of Wealth Management Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 263,320	$ 225,768
Wealth Management
Disaggregation of Revenue [Line Items]
Revenues	144,989	89,532
Wealth Management | Recognized Upon Transaction
Disaggregation of Revenue [Line Items]
Revenues	25,240	16,454
Wealth Management | Recognized Over Time
Disaggregation of Revenue [Line Items]
Revenues	119,749	73,078
Wealth Management | Commission revenue
Disaggregation of Revenue [Line Items]
Revenues	50,580	37,160
Wealth Management | Commission revenue | Recognized Upon Transaction
Disaggregation of Revenue [Line Items]
Revenues	23,381	15,684
Wealth Management | Commission revenue | Recognized Over Time
Disaggregation of Revenue [Line Items]
Revenues	27,199	21,476
Wealth Management | Advisory revenue
Disaggregation of Revenue [Line Items]
Revenues	78,757	39,757
Wealth Management | Advisory revenue | Recognized Upon Transaction
Disaggregation of Revenue [Line Items]
Revenues	0	0
Wealth Management | Advisory revenue | Recognized Over Time
Disaggregation of Revenue [Line Items]
Revenues	78,757	39,757
Wealth Management | Asset-based revenue
Disaggregation of Revenue [Line Items]
Revenues	10,579	9,693
Wealth Management | Asset-based revenue | Recognized Upon Transaction
Disaggregation of Revenue [Line Items]
Revenues	0	0
Wealth Management | Asset-based revenue | Recognized Over Time
Disaggregation of Revenue [Line Items]
Revenues	10,579	9,693
Wealth Management | Transaction and fee revenue
Disaggregation of Revenue [Line Items]
Revenues	5,073	2,922
Wealth Management | Transaction and fee revenue | Recognized Upon Transaction
Disaggregation of Revenue [Line Items]
Revenues	1,859	770
Wealth Management | Transaction and fee revenue | Recognized Over Time
Disaggregation of Revenue [Line Items]
Revenues	$ 3,214	$ 2,152