Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Calculations for basic and diluted earnings per common share
Net income	$ 326,790	$ 333,562	$ 229,264
Preferred stock dividends	(15,202)	(10,784)	(9,347)
Net income available to common equity	311,587	322,779	219,917
Common shareholder dividends	(111,091)	(104,981)	(75,967)
Unvested share-based payment awards	(713)	(537)	(450)
Undistributed earnings	199,784	217,260	143,500
Undistributed earnings allocated to common shareholders	198,424	216,199	142,593
Undistributed earnings allocated to unvested share-based payment awards	1,360	1,060	907
Undistributed earnings	199,784	217,260	143,500
Basic
Distributed earnings to common shareholders	111,091	104,981	75,967
Undistributed earnings allocated to common shareholders	198,424	216,199	142,593
Total common shareholders earnings, basic	309,514	321,181	218,560
Diluted
Distributed earnings to common shareholders	111,091	104,981	75,967
Undistributed earnings allocated to common shareholders	198,424	216,199	142,593
Total common shareholders earnings, diluted	$ 309,514	$ 321,181	$ 218,560
Weighted average common shares outstanding	160,534	167,345	150,877
Effect of dilutive common stock awards	1,398	1,985	2,038
Effect of dilutive common stock warrants	0	402	732
Diluted weighted average common shares outstanding	161,932	169,732	153,647
Basic earnings per common share	$ 1.93	$ 1.92	$ 1.45
Diluted earnings per common share	$ 1.91	$ 1.89	$ 1.42