Shareholders' Equity Shareholders' Equity Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended															12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Option Plan																	101,165,000	84,686,000
Net Income	$ 30,496	$ 31,737	[1]	$ 29,763	[1]	$ 27,560	[1]	$ 27,030	[1]	$ 28,996	[1]	$ 31,493	[1]	$ 15,390	[1]	$ 119,558	$ 102,909	$ 82,170
Less: preferred dividend																		6,167
Less: accretion of preferred stock discount																		204
Net income available to common shareholders																119,558	102,909	75,799
Weighted average number of common shares outstanding - basic																109,102,000	101,163,000	84,678,000
Earnings Per Share, Basic	$ 0.28	$ 0.29		$ 0.27		$ 0.25		$ 0.25		$ 0.27		$ 0.32		$ 0.18		$ 1.10	$ 1.02	$ 0.90
Income used in diluted earnings per share calculation																$ 119,558	$ 102,909	$ 75,799
Average common and common stock equivalent share outstanding																109,102,000	101,165,000	84,686,000
Earnings Per Share, Diluted	$ 0.28	$ 0.29		$ 0.27		$ 0.25		$ 0.25		$ 0.27		$ 0.32		$ 0.18		$ 1.10	$ 1.02	$ 0.90
Options to Purchase Shares																3,400,000	4,400,000	4,900,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Option Plan																0	2,000	8,000
Non stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Option Plan																109,102,000	101,163,000	84,678,000

[1] * Net income restated to reflect purchase accounting adjustments which decreased the bargain purchase gain recognized on the George Washington acquisition to $1.0 million in the quarter ended March 31, 2010.