Short-Term Borrowings (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-term Debt [Line Items]
Balance at year-end	$ 181,592,000	$ 159,434,000
FHLB, unused lines of credit available for short-term financing	323,000,000	284,000,000
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Balance at year-end	27,000,000	0	0
Average during the year	3,017,000	0	5,957,000
Maximum month end balance	28,000,000	0	50,000,000
Weighted average rate during the year (in hundredths)	0.11%	0.00%	0.30%
Weighted average rate at December 31 (in hundredths)	0.13%	0.00%	0.00%
Securities Sold under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Balance at year-end	154,592,000	159,184,000	155,727,000
Average during the year	150,663,000	157,964,000	133,859,000
Maximum month end balance	178,414,000	169,278,000	166,208,000
Weighted average rate during the year (in hundredths)	0.13%	0.25%	0.40%
Weighted average rate at December 31 (in hundredths)	0.10%	0.15%	0.32%
Other Short-Term Borrowings [Member]
Short-term Debt [Line Items]
Balance at year-end	0	250,000	250,000
Average during the year	249,000	250,000	250,000
Maximum month end balance	$ 250,000	$ 250,000	$ 250,000
Weighted average rate during the year (in hundredths)	0.00%	0.00%	0.03%
Weighted average rate at December 31 (in hundredths)	0.00%	0.00%	0.00%