Short-Term Borrowings (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Short-term Debt [Line Items]
Balance at year-end	$ 162,941,000	$ 181,592,000
FHLB, unused lines of credit available for short-term financing	418,000,000	323,000,000
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Balance at year-end	10,000,000	27,000,000	0
Average during the year	12,658,000	3,017,000	0
Maximum month end balance	60,000,000	28,000,000	0
Weighted average rate during the year (in hundredths)	0.27%	0.11%	0.00%
Weighted average rate at December 31 (in hundredths)	0.27%	0.13%	0.00%
Securities Sold under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Balance at year-end	152,941,000	154,592,000	159,184,000
Average during the year	153,084,000	150,663,000	157,964,000
Maximum month end balance	165,977,000	178,414,000	169,278,000
Weighted average rate during the year (in hundredths)	0.10%	0.13%	0.25%
Weighted average rate at December 31 (in hundredths)	0.10%	0.10%	0.15%
Other Short-Term Borrowings [Member]
Short-term Debt [Line Items]
Balance at year-end	0	0	250,000
Average during the year	0	249,000	250,000
Maximum month end balance	$ 0	$ 250,000	$ 250,000
Weighted average rate during the year (in hundredths)	0.00%	0.00%	0.00%
Weighted average rate at December 31 (in hundredths)	0.00%	0.00%	0.00%