Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Calculations for basic and diluted earnings per common share
Net income	$ 45,199	$ 47,388
Preferred stock dividends and discount accretion	(1,244)	(1,300)
Net income available to common equity	43,955	46,088
Common shareholder dividends	(14,488)	(13,377)
Unvested share-based payment awards	(151)	(107)
Undistributed earnings	29,316	32,604
Undistributed earnings allocated to common shareholders	29,126	32,375
Undistributed earnings allocated to unvested share-based payment awards	190	229
Undistributed earnings	29,316	32,604
Basic
Distributed earnings to common shareholders	14,488	13,377
Undistributed earnings allocated to common shareholders	29,126	32,375
Total common shareholders earnings, basic	43,614	45,752
Diluted
Distributed earnings to common shareholders	14,488	13,377
Undistributed earnings allocated to common shareholders	29,126	32,375
Total common shareholders earnings, diluted	$ 43,614	$ 45,752
Weighted average common shares outstanding	161,467,000	168,234,000
Effect of dilutive common stock awards	721,000	170,000
Diluted weighted average common shares outstanding	162,188,000	168,404,000
Basic earnings per common share	$ 0.27	$ 0.27
Diluted earnings per common share	$ 0.27	$ 0.27
Earnings Per Share (Textuals) [Abstract]
Number of antidilutive stock options excluded from the computation of diluted earnings per share	3,000,000	3,000,000