Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Calculations for basic and diluted earnings per common share
Net income	$ 45,838	$ 86,686
Preferred stock dividends	(3,801)	(3,801)
Net income available to common equity	42,037	82,885
Common shareholder dividends	(28,264)	(28,080)
Unvested share-based payment awards	(128)	(103)
Undistributed earnings	13,645	54,702
Undistributed earnings allocated to common shareholders	13,555	54,410
Undistributed earnings allocated to unvested share-based payment awards	90	292
Undistributed earnings	13,645	54,702
Basic
Distributed earnings to common shareholders	28,264	28,080
Undistributed earnings allocated to common shareholders	13,555	54,410
Total common shareholders earnings, basic	41,819	82,490
Diluted
Distributed earnings to common shareholders	28,264	28,080
Undistributed earnings allocated to common shareholders	13,555	54,410
Total common shareholders earnings, diluted	$ 41,819	$ 82,490
Weighted average common shares outstanding	154,701	163,928
Effect of dilutive common stock awards	918	1,505
Diluted weighted average common shares outstanding	155,619	165,433
Basic earnings per common share	$ 0.27	$ 0.50
Diluted earnings per common share	$ 0.27	$ 0.50