Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Calculations for basic and diluted earnings per common share
Net income	$ 45,658	$ 46,395	$ 140,934	$ 132,345
Preferred stock dividends and discount accretion	(1,285)	(1,300)	(3,885)	(3,900)
Net income available to common equity	44,373	45,095	137,049	128,445
Common shareholder dividends	(13,167)	(8,594)	(39,849)	(25,893)
Unvested share-based payment awards	(100)	(36)	(374)	(116)
Undistributed earnings	31,106	36,465	96,826	102,436
Undistributed earnings allocated to common shareholders	30,873	36,311	96,112	101,975
Undistributed earnings allocated to unvested share-based payment awards	233	154	714	461
Undistributed earnings	31,106	36,465	96,826	102,436
Basic
Distributed earnings to common shareholders	13,167	8,594	39,849	25,893
Undistributed earnings allocated to common shareholders	30,873	36,311	96,112	101,975
Total common shareholders earnings, basic	44,040	44,905	135,961	127,868
Diluted
Distributed earnings to common shareholders	13,167	8,594	39,849	25,893
Undistributed earnings allocated to common shareholders	30,873	36,311	96,112	101,975
Total common shareholders earnings, diluted	$ 44,040	$ 44,905	$ 135,961	$ 127,868
Weighted average common shares outstanding	164,954,000	171,650,000	166,586,000	172,774,000
Effect of dilutive common stock awards	489,000	130,000	174,000	74,000
Diluted weighted average common shares outstanding	165,443,000	171,780,000	166,760,000	172,848,000
Basic earnings per common share	$ 0.27	$ 0.26	$ 0.82	$ 0.74
Diluted earnings per common share	$ 0.27	$ 0.26	$ 0.82	$ 0.74
Earnings Per Share (Textuals) [Abstract]
Number of antidilutive stock options excluded from the computation of diluted earnings per share	3,000,000	9,000,000	3,000,000	6,000,000