Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										$ 891,586
Interest										52,484	$ 48,498	$ 47,649
Principal transactions, net										(14,461)	(23,273)	(20,481)
Revenues, Excluding Revenue From Contract With Customers, Other										(377)
Revenues, Excluding Revenue From Contract With Customers										(66,568)
Revenue		$ (243,254)	$ (237,814)	$ (242,556)	$ (234,530)	$ (264,973)	$ (226,220)	$ (215,884)	$ (213,261)	(958,154)	(920,338)	(857,779)
Commissions From Sales And Trading [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										286,211
Mutual Fund Income [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										43,457
Advisory Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										314,349
Investment Banking, Capital Markets [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										69,758
Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										45,595
Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										116,052
Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										16,164
Private Client Division
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										584,236
Interest										37,581
Principal transactions, net										1,125
Revenues, Excluding Revenue From Contract With Customers, Other										2,821
Revenues, Excluding Revenue From Contract With Customers										(33,635)
Revenue	[1]									(617,871)	(592,753)	(504,192)
Private Client Division | Commissions From Sales And Trading [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										154,167
Private Client Division | Mutual Fund Income [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										42,514
Private Client Division | Advisory Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										243,474
Private Client Division | Investment Banking, Capital Markets [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										13,284
Private Client Division | Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Private Client Division | Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										116,052
Private Client Division | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										14,745
Asset Management Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										71,696
Interest										0
Principal transactions, net										0
Revenues, Excluding Revenue From Contract With Customers, Other										0
Revenues, Excluding Revenue From Contract With Customers										0
Revenue	[1]									(71,696)	(89,896)	(92,852)
Asset Management Segment [Member] | Commissions From Sales And Trading [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Asset Management Segment [Member] | Mutual Fund Income [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										908
Asset Management Segment [Member] | Advisory Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										70,775
Asset Management Segment [Member] | Investment Banking, Capital Markets [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Asset Management Segment [Member] | Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Asset Management Segment [Member] | Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Asset Management Segment [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										13
Capital markets
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										235,158
Interest										13,739
Principal transactions, net										(23,378)
Revenues, Excluding Revenue From Contract With Customers, Other										(444)
Revenues, Excluding Revenue From Contract With Customers										(37,561)
Revenue										(272,719)	(231,632)	(254,933)
Capital markets | Commissions From Sales And Trading [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										131,955
Capital markets | Mutual Fund Income [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										13
Capital markets | Advisory Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										67
Capital markets | Investment Banking, Capital Markets [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										56,474
Capital markets | Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										45,595
Capital markets | Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Capital markets | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										1,054
Corporate/Other
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										496
Interest										1,164
Principal transactions, net										(7,792)
Revenues, Excluding Revenue From Contract With Customers, Other										(2,000)
Revenues, Excluding Revenue From Contract With Customers										(4,628)
Revenue										(4,132)	$ (6,057)	$ (5,802)
Corporate/Other | Commissions From Sales And Trading [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										89
Corporate/Other | Mutual Fund Income [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										22
Corporate/Other | Advisory Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										33
Corporate/Other | Investment Banking, Capital Markets [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Corporate/Other | Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Corporate/Other | Investment Banking, Advisory [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0
Corporate/Other | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										$ 352

[1] Clients investing in the OAM advisory program are charged fees based on the value of AUM. Advisory fees were allocated 22.5% to the Asset Management and 77.5% to the Private Client segments. Starting January 1, 2017, the Company determined it was appropriate to change the allocation to 10.0% to the Asset Management and 90.0% to the Private Client segments due to changes in the mix of the business over time and costs associated with it.