Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Calculations for basic and diluted earnings per common share
Net income	$ 94,301	$ 45,838
Preferred stock dividends	(5,207)	(3,801)
Net income available to common equity	89,094	42,037
Common shareholder dividends	(27,661)	(28,264)
Unvested share-based payment awards	(209)	(128)
Undistributed earnings	61,224	13,645
Undistributed earnings allocated to common shareholders	60,836	13,555
Undistributed earnings allocated to unvested share-based payment awards	387	90
Undistributed earnings	61,224	13,645
Basic
Distributed earnings to common shareholders	27,661	28,264
Undistributed earnings allocated to common shareholders	60,836	13,555
Total common shareholders earnings, basic	88,497	41,819
Diluted
Distributed earnings to common shareholders	27,661	28,264
Undistributed earnings allocated to common shareholders	60,836	13,555
Total common shareholders earnings, diluted	$ 88,497	$ 41,819
Weighted average common shares outstanding	152,355	154,701
Effect of dilutive common stock awards	1,333	918
Diluted weighted average common shares outstanding	153,688	155,619
Basic earnings per common share	$ 0.58	$ 0.27
Diluted earnings per common share	$ 0.58	$ 0.27