Segment Information - Reported Revenue and Profit Before Income Taxes (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
Revenue
Total revenue		$ (243,254)	$ (237,814)	$ (242,556)	$ (234,530)	$ (264,973)	$ (226,220)	$ (215,884)	$ (213,261)	$ (958,154)	$ (920,338)	$ (857,779)
Income (loss) before income taxes
Income (loss) before income taxes from continuing operations		$ 15,583	$ 7,144	$ 12,501	$ 9,625	$ 16,570	$ 11,828	$ (1,637)	$ (7,025)	44,853	19,736	(21,892)
Private Client Division
Revenue
Total revenue	[1]									(617,871)	(592,753)	(504,192)
Income (loss) before income taxes
Income (loss) before income taxes from continuing operations	[1]									$ 149,097	$ 128,840	$ 66,072
Asset management fees										90.00%	90.00%	77.50%
Asset Management
Revenue
Total revenue	[1]									$ (71,696)	$ (89,896)	$ (92,852)
Income (loss) before income taxes
Income (loss) before income taxes from continuing operations	[1]									$ 18,590	$ 26,685	$ 31,412
Asset management fees										10.00%	10.00%	22.50%
Capital markets
Revenue
Total revenue										$ (272,719)	$ (231,632)	$ (254,933)
Income (loss) before income taxes
Income (loss) before income taxes from continuing operations										(13,416)	(39,978)	(17,713)
Corporate/Other
Revenue
Total revenue										(4,132)	(6,057)	(5,802)
Income (loss) before income taxes
Income (loss) before income taxes from continuing operations										$ (109,418)	$ (95,811)	$ (101,663)

[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.