Short-Term Borrowings (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Securities sold under agreements to repurchase
Outstanding balance at end of period	$ 60,031,000	$ 72,569,000
Average interest rate at end of period	0.26%	0.31%
Average daily balance during the period	60,234,000	80,137,000
Average interest rate during the period	0.29%	0.51%
Maximum daily balance during the period	$ 73,054,000	$ 116,397,000