Borrowings (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jun. 30, 2007	Jun. 30, 2006
Borrowings (Textual) [Abstract]
FHLB advances	$ 448,700,000	$ 548,400,000
Weighted average interest rate	3.89%	3.71%
Average outstanding balance	548,000,000	790,600,000
Maximum Outstanding Balance	548,600,000	998,100,000
Prepayment Penalties on Borrowing	3,300,000	18,700,000	4,400,000
Securities purchased					250,000,000
Debt funded at Repurchase agreement					250,000,000
Maturity date	Sep. 30, 2012
Fund borrowed under repurchase agreement	509,400,000	542,200,000
Weighted average interest rate	0.35%	0.55%
Maximum amount of accumulated federal tax deposit	15,000,000
Federal tax deposits	9,111,000	30,053,000	30,748,000
Subordinated debt				$ 5,000,000
Variable interest rate	1.65%
Subordinated debt, callable date	Jan. 07, 2011