Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Calculations for basic and diluted earnings per common share
Net income	$ 42,534	$ 46,672
Preferred stock dividends	(2,198)	(1,228)
Net income available to common equity	40,336	45,444
Common shareholder dividends	(16,203)	(15,166)
Unvested share-based payment awards	(206)	(114)
Undistributed earnings	23,927	30,164
Undistributed earnings allocated to common shareholders	23,686	29,886
Undistributed earnings allocated to unvested share-based payment awards	241	278
Undistributed earnings	23,927	30,164
Basic
Distributed earnings to common shareholders	16,203	15,166
Undistributed earnings allocated to common shareholders	23,686	29,886
Total common shareholders earnings, basic	39,889	45,052
Diluted
Distributed earnings to common shareholders	16,203	15,166
Undistributed earnings allocated to common shareholders	23,686	29,886
Total common shareholders earnings, diluted	$ 39,889	$ 45,052
Weighted average common shares outstanding (in shares)	148,601	150,070
Effect of dilutive common stock awards (in shares)	853	1,094
Diluted weighted average common shares outstanding (in shares)	149,454	151,164
Basic earnings (loss) per common share (in usd per share)	$ 0.27	$ 0.30
Diluted earnings (loss) per common share (in usd per share)	$ 0.27	$ 0.30
Earnings Per Share (Textuals) [Abstract]
Number of antidilutive stock options excluded from the computation of diluted earnings per share (in shares)	3,000	2,000
Warrants to purchase	4,000	4,000