Fair Value Measurements - Valuation Techniques and Inputs (Details) - Significant Unobservable Inputs (Level 3) $ in Millions	Dec. 31, 2019 USD ($)
CLO equities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 87.6
CLO equities | Valuation Technique, Discounted Cash Flow [Member] | Collateral reinvestment coupon floor
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.01
CLO equities | Minimum | Valuation Technique, Consensus Pricing Model [Member] | Offered quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.14
CLO equities | Minimum | Valuation Technique, Discounted Cash Flow [Member] | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.10
CLO equities | Minimum | Valuation Technique, Discounted Cash Flow [Member] | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.50
CLO equities | Minimum | Valuation Technique, Discounted Cash Flow [Member] | Prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.20
CLO equities | Maximum | Valuation Technique, Consensus Pricing Model [Member] | Offered quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.87
CLO equities | Maximum | Valuation Technique, Discounted Cash Flow [Member] | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.30
CLO equities | Maximum | Valuation Technique, Discounted Cash Flow [Member] | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.70
CLO equities | Maximum | Valuation Technique, Discounted Cash Flow [Member] | Prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.30
CLO equities | Weighted Average | Valuation Technique, Consensus Pricing Model [Member] | Offered quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.48
CLO equities | Weighted Average | Valuation Technique, Discounted Cash Flow [Member] | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.195
CLO equities | Weighted Average | Valuation Technique, Discounted Cash Flow [Member] | Prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.25
Private equity funds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 268.8
Private equity funds | Minimum | Transactional value | Implied price at recent purchase transaction
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.135
Private equity funds | Maximum | Transactional value | Implied price at recent purchase transaction
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative investments, measurement input	0.1385