Significant Transactions - MediaAlpha (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Mar. 23, 2021	Oct. 30, 2020	Mar. 31, 2022
Other Significant Noncash Transactions [Line Items]
Increase in book value per share (in dollars per share)			$ 5.65
IPO | Marketing Technology (MediaAlpha)
Other Significant Noncash Transactions [Line Items]
Sale of stock, price per share (in usd per share)		$ 19.00
Sale of stock, price per share, net of underwriting fees (in USD per share)		$ 17.67
Secondary Offering | Marketing Technology (MediaAlpha)
Other Significant Noncash Transactions [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	8,050,000.00
Sale of stock, price per share (in usd per share)	$ 46.00
Sale of stock, price per share, net of underwriting fees (in USD per share)	$ 44.62
Marketing Technology (MediaAlpha)
Other Significant Noncash Transactions [Line Items]
Proceeds from dividends received		$ 55.0
Increase in investment owned (in dollars per share)			1.00
Share price (in usd per share)			$ 16.55
Investment owned, balance			$ 280.4
Marketing Technology (MediaAlpha) | IPO
Other Significant Noncash Transactions [Line Items]
Sale of stock, number of shares issued in transaction (in shares)		3,600,000
Sale of stock, consideration received in transaction		$ 63.8
Investment owned (in shares)			16,900,000
Ownership interest (as a percent)			27.70%
Fully diluted ownership interest (as a percent)			25.00%
Share price (in usd per share)			$ 16.55
Marketing Technology (MediaAlpha) | Secondary Offering
Other Significant Noncash Transactions [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	3,600,000
Sale of stock, consideration received in transaction	$ 160.3