Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Calculations for basic and diluted earnings per common share
Net income	$ 46,365	$ 47,888	$ 91,564	$ 95,276
Preferred stock dividends and discount accretion	(1,278)	(1,300)	(2,522)	(2,600)
Net income available to common equity	45,087	46,588	89,042	92,676
Common shareholder dividends	(14,393)	(13,305)	(28,881)	(26,682)
Unvested share-based payment awards	(143)	(168)	(294)	(275)
Undistributed earnings	30,551	33,115	59,867	65,719
Undistributed earnings allocated to common shareholders	30,247	32,864	59,375	65,239
Undistributed earnings allocated to unvested share-based payment awards	304	251	492	480
Undistributed earnings	30,551	33,115	59,867	65,719
Basic
Distributed earnings to common shareholders	14,393	13,305	28,881	26,682
Undistributed earnings allocated to common shareholders	30,247	32,864	59,375	65,239
Total common shareholders earnings, basic	44,640	46,169	88,256	91,921
Diluted
Distributed earnings to common shareholders	14,393	13,305	28,881	26,682
Undistributed earnings allocated to common shareholders	30,247	32,864	59,375	65,239
Total common shareholders earnings, diluted	$ 44,640	$ 46,169	$ 88,256	$ 91,921
Weighted average common shares outstanding	159,940,000	166,605,000	160,699,000	167,415,000
Effect of dilutive common stock awards	898,000	143,000	814,000	137,000
Diluted weighted average common shares outstanding	160,838,000	166,748,000	161,513,000	167,552,000
Basic earnings per common share	$ 0.28	$ 0.28	$ 0.55	$ 0.55
Diluted earnings per common share	$ 0.28	$ 0.28	$ 0.55	$ 0.55
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	2,000,000	3,000,000