Note 8 - Changes in Accumulated Other Comprehensive Income (Loss) By Component (1) - Accumulated Other Comprehensive Loss (Details) - USD ($)		3 Months Ended		6 Months Ended				12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017		Dec. 31, 2017
Balance				$ 226,460,000		$ 215,053,000		$ 215,053,000
Reclassification due to the adoption of ASU 2018-02								1,600,000
Unrealized loss on securities		$ (1,796,000)	$ 1,097,000	(7,035,000)		1,720,000
Net current-period other comprehensive income (loss)		(1,773,000)	1,125,000	(6,981,000)		1,775,000
Balance		235,334,000	222,321,000	235,334,000		222,321,000		226,460,000
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Balance	[1]			(7,150,000)		(6,831,000)		(6,831,000)
Reclassification due to the adoption of ASU 2018-02	[1]			(1,562,000)
Unrealized loss on securities				(7,036,000)	[1]	1,681,000	[1]	(413,000)
Amounts reclassified from accumulated other comprehensive income to net income (2)	[1],[2]			1,000		39,000		94,000
Net current-period other comprehensive income (loss)	[1]			(7,035,000)		1,720,000		(319,000)
Balance	[1]	(15,747,000)	(5,111,000)	(15,747,000)		(5,111,000)		(7,150,000)
Accumulated Net Investment Gain (Loss) on Securities Transferred from Available-for-Sale to Held-to-Maturity [Member]
Balance	[1]			(359,000)		(463,000)		(463,000)
Reclassification due to the adoption of ASU 2018-02	[1]			(78,000)
Unrealized loss on securities					[1]		[1]
Amounts reclassified from accumulated other comprehensive income to net income (2)	[1],[2]			54,000		55,000		104,000
Net current-period other comprehensive income (loss)	[1]			54,000		55,000		104,000
Balance	[1]	(383,000)	(408,000)	(383,000)		(408,000)		(359,000)
AOCI Attributable to Parent [Member]
Balance	[1]			(7,509,000)		(7,294,000)		(7,294,000)
Reclassification due to the adoption of ASU 2018-02	[1]			(1,640,000)
Unrealized loss on securities				(7,036,000)	[1]	1,681,000	[1]	(413,000)
Amounts reclassified from accumulated other comprehensive income to net income (2)	[1],[2]			55,000		94,000		198,000
Net current-period other comprehensive income (loss)	[1]			(6,981,000)		1,775,000		(215,000)
Balance	[1]	$ (16,130,000)	$ (5,519,000)	$ (16,130,000)		$ (5,519,000)		$ (7,509,000)

[1] All amounts are net of tax. Amounts in parentheses indicate reductions to other comprehensive income.

[2] Reclassification amounts are reported as gains on sales of investment securities, impairment losses, and amortization of net unrealized losses on the Consolidated Statement of Operations.