COST-SAVING INITIATIVES - Expenses Associated with Cost Savings Initiatives (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Cost Saving initiatives [Line Items]
Restructuring charges	$ 146,705	$ 48,729	$ 167,445
Severance and other employee termination expenses (included in "compensation and benefits" expense)
Cost Saving initiatives [Line Items]
Restructuring charges	136,608	46,610	157,348
Technology asset impairments (included in "technology and information services")
Cost Saving initiatives [Line Items]
Restructuring charges	7,385		7,385
Other
Cost Saving initiatives [Line Items]
Restructuring charges	2,712	2,119	2,712
Operating Segments | Financial Advisory
Cost Saving initiatives [Line Items]
Restructuring charges	81,876	33,481	90,653
Operating Segments | Financial Advisory | Severance and other employee termination expenses (included in "compensation and benefits" expense)
Cost Saving initiatives [Line Items]
Restructuring charges	81,266	32,773	90,043
Operating Segments | Financial Advisory | Technology asset impairments (included in "technology and information services")
Cost Saving initiatives [Line Items]
Restructuring charges	88		88
Operating Segments | Financial Advisory | Other
Cost Saving initiatives [Line Items]
Restructuring charges	522	708	522
Operating Segments | Asset Management
Cost Saving initiatives [Line Items]
Restructuring charges	37,110	11,559	48,345
Operating Segments | Asset Management | Severance and other employee termination expenses (included in "compensation and benefits" expense)
Cost Saving initiatives [Line Items]
Restructuring charges	29,533	11,545	40,768
Operating Segments | Asset Management | Technology asset impairments (included in "technology and information services")
Cost Saving initiatives [Line Items]
Restructuring charges	7,297		7,297
Operating Segments | Asset Management | Other
Cost Saving initiatives [Line Items]
Restructuring charges	280	14	280
Corporate
Cost Saving initiatives [Line Items]
Restructuring charges	27,719	3,689	28,447
Corporate | Severance and other employee termination expenses (included in "compensation and benefits" expense)
Cost Saving initiatives [Line Items]
Restructuring charges	25,809	2,292	26,537
Corporate | Technology asset impairments (included in "technology and information services")
Cost Saving initiatives [Line Items]
Restructuring charges	0		0
Corporate | Other
Cost Saving initiatives [Line Items]
Restructuring charges	$ 1,910	$ 1,397	$ 1,910