Derivatives (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011
Derivatives (Textual) [Abstract]
Number of interest rate swaps with an aggregate notional amount	1
Notional amount of interest rate derivatives	$ 541,800,000
Derivative, net hedge ineffectiveness gain (loss)	0
Termination value of derivatives in a net liability position	12,200,000
Collateral obligations for derivative counterparties	11,600,000
Interest rate swap [Member]
Derivatives (Textual) [Abstract]
Notional amount of interest rate derivatives	$ 140,000,000