Capital Ratios (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Capital Ratios
Tier 1 Capital (to Average Assets), Actual Ratio (as a percent)	11.38%	10.86%
Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent)	20.31%	19.65%
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent)	21.36%	20.60%
Identified intangibles and goodwill	$ 289,214,000
Percentage of capital securities issued by trust qualifying as Tier I capital, maximum	25.00%
Capital securities issued by the trust, qualifying as Tier I capital	$ 190,726,000	$ 190,726,000