Material Transactions Affecting Stockholders' Equity (Details) - USD ($)		3 Months Ended	6 Months Ended
	Mar. 09, 2020	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Mar. 19, 2020	Feb. 26, 2020	Feb. 25, 2020
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		231,000	231,000
Preferred stock issued		$ 221,312,000	$ 221,312,000
Net proceeds from the issuance of preferred stock		$ 221,300,000	$ 221,312,000	$ 0
Stock repurchase program, authorized amount					$ 180,000,000	$ 200,000,000	$ 180,000,000
Common stock repurchased (in shares)		1,200,000
Total cost of common stock repurchased		$ 22,600,000
Depository Series A Shares
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		4,300,000	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	4,900,000
Preferred stock, conversion rate (as a percent)		2.50%
Depository Shares
Class of Stock [Line Items]
Preferred stock issued		$ 230,500,000
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