Fair Value Measurements - Quantitative Information used in Valuing Level 3 Liabilities (Details) - Affiliate Equity Repurchase Obligations - Discounted cash flow $ in Millions		Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Growth rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input		0.01	(0.09)
Growth rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input		0.10	0.07
Growth rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	[1]	0.08	0.05
Discount rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input		0.15	0.14
Discount rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input		0.16	0.17
Discount rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	[1]	0.15	0.15
Significant Unobservable Inputs (Level 3)
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair Value		$ 115.1	$ 19.8

[1] Represents growth rates of asset and performance based fees.