Off-Balance Sheet Credit Risk (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Fair value of securities accepted as collateral permitted to sell or repledge	$ 1,100,000,000	$ 1,000,000,000
Fair value of collateral securities sold or repledged	153,300,000	80,200,000
Outstanding commitments to originate loans	330,300,000	141,000,000
Letters of credit outstanding	10,500,000	9,200,000
Unused lines of Credit [Member]
Unused lines of credit to commercial and consumer borrowers	$ 477,000,000	$ 102,400,000