Note 4 -Gross Realized Losses on Equity and Debt Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Gain Loss On Investments Including Marketable Securities And Investments Held At Cost Income Statement Reported Amounts Summary [Line Items]
Gross realized gains	$ 2,138	$ 939	$ 943
Gross realized losses	(558)	(73)	(105)
Other-than-temporary impairment losses	(80)	(192)	(55)
Net gain on investment securities	1,500	674	783
Equity Securities [Member]
Schedule Of Gain Loss On Investments Including Marketable Securities And Investments Held At Cost Income Statement Reported Amounts Summary [Line Items]
Gross realized gains	1,557	758	714
Gross realized losses	0	0	(23)
Other-than-temporary impairment losses	(80)	(192)	(55)
Net gain on investment securities	1,477	566	636
Debt Securities [Member]
Schedule Of Gain Loss On Investments Including Marketable Securities And Investments Held At Cost Income Statement Reported Amounts Summary [Line Items]
Gross realized gains	581	181	229
Gross realized losses	(558)	(73)	(82)
Other-than-temporary impairment losses	0	0	0
Net gain on investment securities	$ 23	$ 108	$ 147