Note 9 - Borrowed Funds - Comparative Data for Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Average amount outstanding during the year (1)	[1]	$ 136,849	$ 381,967	$ 400,822
Maximum amount outstanding at month-end (2)	[2]	150,000	400,000	400,000
Balance, December 31		$ 100,000	$ 350,000	$ 400,000
Rate, December 31		2.86%	4.06%	3.89%
Weighted average interest rate for the year		3.11%	4.01%	3.95%

[1] Average balances were computed using daily averages.

[2] Highest month-end balances were January 2017, January 2016, and January 2015.