Short-Term Borrowings (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Securities sold under agreements to repurchase
Outstanding balance at year end	$ 64,765,000	$ 72,569,000
Weighted average interest rate at year end	0.13%	0.31%
Average daily balance during the year	61,930,000	80,137,000
Weighted average interest rate during the year	0.25%	0.51%
Maximum daily balance during the year	$ 81,980,000	$ 116,397,000