COST-SAVING INITIATIVES - Expenses Associated with Cost Savings Initiatives (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Cost Saving initiatives [Line Items]
Restructuring charges	$ 15,707	$ 48,729	$ 183,152
Severance and other employee termination expenses (included in "compensation and benefits" expense)
Cost Saving initiatives [Line Items]
Restructuring charges	8,941	46,610	166,289
Technology asset impairments (included in "technology and information services")
Cost Saving initiatives [Line Items]
Restructuring charges	571		7,956
Foreign exchange related losses associated with closing of certain offices (included in "revenue other")
Cost Saving initiatives [Line Items]
Restructuring charges	4,647		4,647
Other
Cost Saving initiatives [Line Items]
Restructuring charges	1,548	2,119	4,260
Operating Segments | Financial Advisory
Cost Saving initiatives [Line Items]
Restructuring charges	3,677	33,481	94,330
Operating Segments | Financial Advisory | Severance and other employee termination expenses (included in "compensation and benefits" expense)
Cost Saving initiatives [Line Items]
Restructuring charges	(21)	32,773	90,022
Operating Segments | Financial Advisory | Technology asset impairments (included in "technology and information services")
Cost Saving initiatives [Line Items]
Restructuring charges	56		144
Operating Segments | Financial Advisory | Foreign exchange related losses associated with closing of certain offices (included in "revenue other")
Cost Saving initiatives [Line Items]
Restructuring charges	2,164		2,164
Operating Segments | Financial Advisory | Other
Cost Saving initiatives [Line Items]
Restructuring charges	1,478	708	2,000
Operating Segments | Asset Management
Cost Saving initiatives [Line Items]
Restructuring charges	4,733	11,559	53,078
Operating Segments | Asset Management | Severance and other employee termination expenses (included in "compensation and benefits" expense)
Cost Saving initiatives [Line Items]
Restructuring charges	4,190	11,545	44,958
Operating Segments | Asset Management | Technology asset impairments (included in "technology and information services")
Cost Saving initiatives [Line Items]
Restructuring charges	515		7,812
Operating Segments | Asset Management | Foreign exchange related losses associated with closing of certain offices (included in "revenue other")
Cost Saving initiatives [Line Items]
Restructuring charges	0		0
Operating Segments | Asset Management | Other
Cost Saving initiatives [Line Items]
Restructuring charges	28	14	308
Corporate
Cost Saving initiatives [Line Items]
Restructuring charges	7,297	3,689	35,744
Corporate | Severance and other employee termination expenses (included in "compensation and benefits" expense)
Cost Saving initiatives [Line Items]
Restructuring charges	4,772	2,292	31,309
Corporate | Technology asset impairments (included in "technology and information services")
Cost Saving initiatives [Line Items]
Restructuring charges	0		0
Corporate | Foreign exchange related losses associated with closing of certain offices (included in "revenue other")
Cost Saving initiatives [Line Items]
Restructuring charges	2,483		2,483
Corporate | Other
Cost Saving initiatives [Line Items]
Restructuring charges	$ 42	$ 1,397	$ 1,952