Securities (Details Textual) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Securities (Textual) [Abstract]
Impairment loss recognized	$ 0		$ 0
Sales of mortgage-backed securities available for sale	0		8,960,000,000
Realized gains on sales of mortgage backed securities available for sale	0		100,000,000
Sales of investment securities available-for-sale	0		80,000,000
Gross realized gains on sales and calls of investment securities available for sale		$ 2,500,000