Note 4 - Fair Value Measurements - Assets Measured at Fair Value on Nonrecurring Basis (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Loans held for sale, Total gains (losses)		$ (2)	$ 45
Mortgage servicing rights, net, Total gains (losses)		0	0
Loans, Total gains (losses)	[1]	(87)	(97)
Real estate, net, Total gains (losses)	[2]	0	0
Total, Total gains (losses)		(89)	(52)
Fair Value, Nonrecurring [Member]
Loans held for sale		3,292	3,444
Mortgage servicing rights, net		1,831	1,855
Loans	[1]	2,671	2,902
Real estate, net	[2]	444	414
Total		8,238	8,615
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Loans held for sale		0	0
Mortgage servicing rights, net		0	0
Loans	[1]	0	0
Real estate, net	[2]	0	0
Total		0	0
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Loans held for sale		3,292	3,444
Mortgage servicing rights, net		1,831	1,855
Loans	[1]	2,671	2,902
Real estate, net	[2]	444	414
Total		8,238	8,615
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Loans held for sale		0	0
Mortgage servicing rights, net		0	0
Loans	[1]	0	0
Real estate, net	[2]	0	0
Total		$ 0	$ 0

[1] Represents carrying value and related write-downs of loans for which adjustments are based on the appraised value of the collateral. The carrying value of loans fully charged-off is zero.

[2] Represents the fair value and related losses of foreclosed real estate and other collateral owned that were measured at fair value subsequent to their initial classification as foreclosed assets.