Material Transactions Affecting Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Mar. 09, 2020	Mar. 31, 2021	Jun. 30, 2020	Dec. 31, 2020	Feb. 26, 2020	Feb. 25, 2020
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		231,000		231,000
Net proceeds from the issuance of preferred stock			$ 221.2
Stock repurchase program, authorized amount					$ 200.0	$ 180.0
Common stock repurchased (in shares)		715,000
Total cost of common stock repurchased		$ 14.9
Depository Series A Shares
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)			4,300,000
Preferred stock, conversion rate (as a percent)			2.50%
Preferred stock, fixed rate (as a percent)			7.00%
Depository Series C Shares
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)			4,900,000
Preferred stock, conversion rate (as a percent)			2.50%
Depository Shares
Class of Stock [Line Items]
Preferred stock issued			$ 230.5
Bankmanagers Corporation
Class of Stock [Line Items]
Acquisitions, net of issuance costs (in shares)	4,930,231
Shares issued (in dollars per share)	$ 14.58