Shareholders' Equity (Details) (USD $)	1 Months Ended	2 Months Ended	12 Months Ended	126 Months Ended
	Feb. 29, 2012	Feb. 29, 2012	Dec. 31, 2011 Y	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Minimum required capital amounts and ratios for well capitalized institutions and the actual capital amounts
Shareholders' Equity			$ 1,002,667,000	$ 1,002,667,000	$ 1,011,133,000	$ 895,973,000	$ 790,704,000
Tier 1 Capital			903,173,000	903,173,000	928,158,000
Total Capital			971,797,000	971,797,000	992,722,000
Well Capitalized Minimum Tier 1 Capital Ratio (as a percent)			6.00%	6.00%	6.00%
Tier 1 Capital Ratio (as a percent)			16.68%	16.68%	18.28%
Well Capitalized Minimum Total Capital Ratio (as a percent)			10.00%	10.00%	10.00%
Total Capital Ratio (as a percent)			17.95%	17.95%	19.55%
Well Capitalized Minimum Tier 1 Leverage Ratio (as a percent)			5.00%	5.00%	5.00%
Tier 1 Leverage Ratio (as a percent)			6.73%	6.73%	7.15%
Dividends
Number of prior calendar years considered for payment of dividends in excess of the sum of net income			2
Common Stock Repurchase Program
Number of shares of common stock repurchased		190,000	2,500,000	48,500,000
Amount returned to shareholders on stock repurchase		8,800,000	109,900,000	1,700,000,000
Average cost of shares repurchased (in dollars per share)		$ 46.41	$ 43.88	$ 35.98
Remaining buyback authority	65,200,000			74,000,000
Bank
Minimum required capital amounts and ratios for well capitalized institutions and the actual capital amounts
Shareholders' Equity			926,673,000	926,673,000	901,141,000
Tier 1 Capital			841,308,000	841,308,000	832,295,000
Total Capital			$ 909,838,000	$ 909,838,000	$ 896,770,000
Tier 1 Capital Ratio (as a percent)			15.56%	15.56%	16.42%
Total Capital Ratio (as a percent)			16.83%	16.83%	17.69%
Tier 1 Leverage Ratio (as a percent)			6.30%	6.30%	6.46%