Significant Transactions - MediaAlpha (Details) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
	Mar. 23, 2021	Oct. 30, 2020	Feb. 26, 2019	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020
Other Significant Noncash Transactions [Line Items]
Realized gain from transaction				$ 67.5
MediaAlpha
Other Significant Noncash Transactions [Line Items]
Proceeds from dividends received		$ 55.0
Ownership interest (as a percent)		35.00%			28.00%
Fully diluted ownership interest (as a percent)		32.30%			25.70%
Investment owned (in shares)		20,500,000			16,900,000
Share price (in USD per share)					$ 15.44	$ 39.07
Investment owned, balance					$ 261.6	$ 802.2
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
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
MediaAlpha
Other Significant Noncash Transactions [Line Items]
Proceeds from dividends received			$ 89.3
Realized gain from transaction			$ 67.5
Ownership interest (as a percent)			48.30%
Fully diluted ownership interest (as a percent)			42.00%
Assets, fair value			$ 114.7
Unrealized investment gain			114.7
Total realized and unrealized gain on sale of minority stake			$ 182.2
MediaAlpha | Secondary Offering
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 dollars per share)	$ 44.62