Revenue (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Revenue, Major Customer [Line Items]
Total operating revenues	$ 1,659,700,000	$ 1,598,900,000
Deferred carried interest liabilities	59,800,000		$ 58,000,000.0	$ 45,800,000
Performance revenue recognized	0	0
Bermuda
Revenue, Major Customer [Line Items]
Total operating revenues	0	0
Americas
Revenue, Major Customer [Line Items]
Total operating revenues	1,230,400,000	1,180,700,000
UK
Revenue, Major Customer [Line Items]
Total operating revenues	163,700,000	170,800,000
EMEA ex UK (Europe, Middle East and Africa)
Revenue, Major Customer [Line Items]
Total operating revenues	176,400,000	164,400,000
Asia Pacific
Revenue, Major Customer [Line Items]
Total operating revenues	$ 89,200,000	$ 83,000,000.0