Equity-Method Eligible Investments - Significant Equity Method Eligible Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	May 31, 2019	Feb. 26, 2019	Feb. 25, 2019
PassportCard/DavidShield
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	53.80%	50.00%
Stock issued during period, value, acquisitions	$ 15
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	48.30%	48.30%		48.30%	61.00%
durchblicker
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	45.00%	45.00%
Elementum Holdings, L.P.
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	30.00%	30.00%	30.00%
JAM Partners L.P.
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	0.00%	11.10%
Minimum | Tuckerman Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	14.50%	17.50%
Minimum | Enlightenment Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	9.60%	10.00%
Minimum | Kudu Investments
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	3.20%	3.20%
Maximum | Tuckerman Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	62.20%	62.40%
Maximum | Enlightenment Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	66.70%	38.40%
Maximum | Kudu Investments
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	35.00%	30.00%