Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Numerator:
Net income	$ 176,940		$ 220,268		$ 433,416		$ 384,524
Preferred dividends	(5,485)		(7,649)		(10,969)		(14,110)
Loss on repurchase of preferred shares	0		(10,612)		0		(10,612)
Net income available to common shareholders	$ 171,455		$ 202,007		$ 422,447		$ 359,802
Denominator:
Weighted average common shares outstanding — basic	131,377,274		134,529,129		131,143,885		134,241,876
Effect of dilutive common share equivalents:
Nonvested restricted shares	1,088,030		800,455		1,181,947		909,524
Stock options	3,383,746	[1]	2,882,152	[1]	3,298,394	[1]	2,866,090	[1]
Weighted average common shares and common share equivalents outstanding — diluted	135,849,050		138,211,736		135,624,226		138,017,490
Earnings per common share:
Basic (per share)	$ 1.31		$ 1.50		$ 3.22		$ 2.68
Diluted (per share)	$ 1.26		$ 1.46		$ 3.11		$ 2.61
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per common share (shares)	1,428,616		912,056		1,730,313		688,634

[1] Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2013 second quarter and 2012 second quarter, the number of stock options excluded were 1,428,616 and 912,056, respectively. For the six months ended June 30, 2013 and 2012, the number of stock options excluded were 1,730,313 and 688,634, respectively.