Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Calculations for basic and diluted earnings per common share
Net income	$ 47,388	$ 42,633
Preferred stock dividends and discount accretion	(1,300)	(1,300)
Net income available to common equity	46,088	41,333
Common shareholder dividends	(13,377)	(8,683)
Unvested share-based payment awards	(107)	(40)
Undistributed earnings	32,604	32,610
Undistributed earnings allocated to common shareholders	32,375	32,455
Undistributed earnings allocated to unvested share-based payment awards	229	155
Undistributed earnings	32,604	32,610
Basic
Distributed earnings to common shareholders	13,377	8,683
Undistributed earnings allocated to common shareholders	32,375	32,455
Total common shareholders earnings, basic	45,752	41,138
Diluted
Distributed earnings to common shareholders	13,377	8,683
Undistributed earnings allocated to common shareholders	32,375	32,455
Total common shareholders earnings, diluted	$ 45,752	$ 41,138
Weighted average common shares outstanding	168,234,000	173,846,000
Effect of dilutive common stock awards	170,000	2,000
Diluted weighted average common shares outstanding	168,404,000	173,848,000
Basic earnings per common share	$ 0.27	$ 0.24
Diluted earnings per common share	$ 0.27	$ 0.24
Earnings Per Share (Textuals) [Abstract]
Number of antidilutive stock options excluded from the computation of diluted earnings per share	3,000,000	6,000,000