Short-Term Borrowings (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Securities sold under agreements to repurchase
Outstanding balance at end of period	$ 52,831,000	$ 72,569,000
Average interest rate at end of period	0.28%	0.31%
Average daily balance during the period	61,499,000	80,137,000
Average interest rate during the period	0.30%	0.51%
Maximum daily balance during the period	$ 73,054,000	$ 116,397,000