Shareholders' Equity - Preferred Stock and Dividends Paid Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Capital Unit [Line Items]
Preferred stock, shares issued (shares)	5,700,000		5,700,000		9,000,000
Preferred stock, value	$ 137,794		$ 137,794		$ 217,471
Series C Preferred Stock
Capital Unit [Line Items]
Preferred stock, shares issued (shares)	0		0		2,300,000
Preferred stock, value	$ 0		$ 0		$ 55,569
Initial Fixed Rate			7.00%
Preferred stock, dividends, per share, cash paid (usd per share)	$ 0.346206	$ 0.357778	$ 1.041346	$ 1.232778
Series C Preferred Stock | London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Floating rate of Three-Month LIBOR Plus:			5.30%
Series D Preferred Stock
Capital Unit [Line Items]
Preferred stock, shares issued (shares)	0		0		1,000,000
Preferred stock, value	$ 0		$ 0		$ 24,108
Initial Fixed Rate			6.50%
Preferred stock, dividends, per share, cash paid (usd per share)	$ 0.332790	0.40625	$ 1.075982	1.21875
Series D Preferred Stock | London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Floating rate of Three-Month LIBOR Plus:			5.09%
Series E Preferred Stock
Capital Unit [Line Items]
Preferred stock, shares issued (shares)	2,300,000		2,300,000		2,300,000
Preferred stock, value	$ 55,593		$ 55,593		$ 55,593
Initial Fixed Rate			6.45%
Preferred stock, dividends, per share, cash paid (usd per share)	$ 0.335984	0.403125	$ 1.142234	1.209375
Series E Preferred Stock | London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Floating rate of Three-Month LIBOR Plus:			5.14%
Series F Preferred Stock
Capital Unit [Line Items]
Preferred stock, shares issued (shares)	3,400,000		3,400,000		3,400,000
Preferred stock, value	$ 82,201		$ 82,201		$ 82,201
Initial Fixed Rate			6.00%
Preferred stock, dividends, per share, cash paid (usd per share)	$ 0.375	$ 0.375	$ 1.125	$ 1.125
Series F Preferred Stock | London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Floating rate of Three-Month LIBOR Plus:			4.762%