Note 8 - Short-Term Borrowings (Detail) - Short-term Borrowings (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Federal Funds Purchased [Member] | Minimum [Member]
Range of interest rates paid	0.12%	0.07%	0.10%
Federal Funds Purchased [Member] | Maximum [Member]
Range of interest rates paid	0.31%	0.25%	0.35%
Federal Funds Purchased [Member] | At December 31 [Member]
Weighted average interest rate			0.15%
Federal Funds Purchased [Member] | During the Year [Member]
Weighted average interest rate	0.22%	0.13%	0.22%
Federal Funds Purchased [Member]
Balance (in Dollars)			$ 15,000
Weighted average original maturity (days)			1 day
During the year — Maximum month-end balance (in Dollars)	30,000	60,000	105,000
Daily average balance (in Dollars)	10,093	10,926	33,192
Commercial Paper [Member] | Minimum [Member]
Range of interest rates paid	0.25%	0.20%	0.20%
Commercial Paper [Member] | Maximum [Member]
Range of interest rates paid	0.60%	0.60%	0.65%
Commercial Paper [Member] | At December 31 [Member]
Weighted average interest rate	0.32%	0.29%	0.29%
Commercial Paper [Member] | During the Year [Member]
Weighted average interest rate	0.29%	0.30%	0.30%
Commercial Paper [Member]
Balance (in Dollars)	15,345	13,485	14,388
Weighted average original maturity (days)	35 days	44 days	45 days
During the year — Maximum month-end balance (in Dollars)	19,345	16,573	16,927
Daily average balance (in Dollars)	14,826	14,454	14,718
Federal Reserve Bank Advances [Member] | During the Year [Member]
Weighted average interest rate			0.25%
Federal Reserve Bank Advances [Member]
Range of interest rates paid			0.25%
During the year — Maximum month-end balance (in Dollars)			25,000
Daily average balance (in Dollars)			3,699
Treasury Tax and Loan and Term Federal Funds Purchased [Member] | Minimum [Member]
Range of interest rates paid		0.00%	0.00%
Treasury Tax and Loan and Term Federal Funds Purchased [Member] | Maximum [Member]
Range of interest rates paid		0.31%	0.40%
Treasury Tax and Loan and Term Federal Funds Purchased [Member] | During the Year [Member]
Weighted average interest rate		0.07%	0.25%
Treasury Tax and Loan and Term Federal Funds Purchased [Member]
Balance (in Dollars)			3,490
Weighted average original maturity (days)			1 day
During the year — Maximum month-end balance (in Dollars)		23,864	46,779
Daily average balance (in Dollars)		$ 3,666	$ 7,306