Shareholders' Equity - Preferred Stock and Dividends Paid Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Capital Unit [Line Items]
Preferred stock, shares issued	9,000,000	9,000,000
Preferred stock, carrying value	$ 217,471	$ 217,471
Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series C, par value $1.00 per share
Capital Unit [Line Items]
Preferred stock, shares issued	2,300,000	2,300,000
Preferred stock, carrying value	$ 55,569	$ 55,569
Preferred stock, fixed dividend rate	7.00%
Preferred stock, dividends paid (usd per share)	$ 1.58	$ 1.75	$ 1.75
Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series C, par value $1.00 per share | London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Preferred stock, floating dividend rate	5.30%
Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series D, par value $1.00 per share
Capital Unit [Line Items]
Preferred stock, shares issued	1,000,000	1,000,000
Preferred stock, carrying value	$ 24,108	$ 24,108
Preferred stock, fixed dividend rate	6.50%
Preferred stock, dividends paid (usd per share)	$ 1.63	$ 1.63	1.63
Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series D, par value $1.00 per share | London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Preferred stock, floating dividend rate	5.09%
Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series E, par value $1.00 per share
Capital Unit [Line Items]
Preferred stock, shares issued	2,300,000	2,300,000
Preferred stock, carrying value	$ 55,593	$ 55,593
Preferred stock, fixed dividend rate	6.45%
Preferred stock, dividends paid (usd per share)	$ 1.61	$ 1.61	1.61
Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series E, par value $1.00 per share | London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Preferred stock, floating dividend rate	5.14%
Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series F, par value $1.00 per share
Capital Unit [Line Items]
Preferred stock, shares issued	3,400,000	3,400,000
Preferred stock, carrying value	$ 82,201	$ 82,201
Preferred stock, fixed dividend rate	6.00%
Preferred stock, dividends paid (usd per share)	$ 1.50	$ 1.50	$ 1.50
Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series F, par value $1.00 per share | London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Preferred stock, floating dividend rate	4.762%