Fair Value Measurements (Details Textuals) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Fair Value Measurements (Textuals) [Abstract]
Other real estate owned measured at fair value	$ 7,000,000		$ 54,000,000
Write down of Other Real Estate Owned	3,000,000	1,000,000	9,000,000
Notional amount of cash flow hedge interest rate swap agreements	100,000,000
Commitment on standby letters of credit	$ 300,000,000
Weighted average constant prepayment rate	21.55%
Weighted average discount rate	9.70%
Closing ratio	89.00%
3 month LIBOR forward range	0.46% to 3.53%
Significant assumptions on fair value of impaired loans	0% to 50%