Note 5 - Fair Value Measurements and Fair Values of Financial Instruments - Valuation Techniques and the Unobservable Inputs Used in Determining Fair Value - Recurring Basis (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Measurements, Recurring [Member]
Fair value	$ 1,381,000	$ 1,299,000
Valuation Technique, Discounted Cash Flow [Member] | Servicing Rights Assets [Member]
Discount rate	12.50%	13.00%
Weighted-average PSA	121.00%	140.00%
Servicing fees of loan balances	0.25%	0.25%
Servicing fees of payments are late	4.00%	4.00%
Late fees assessed	5.00%	5.00%
Miscellaneous fees per account per month	$ 1.94	$ 1.94
Monthly servicing cost per account	6	6
Additional monthly servicing cost per loan on loans more than 30 days delinquent	$ 24	$ 24
Servicing costs of loans more than 30 days delinquent	1.50%	1.50%
Annual increase in servicing costs	3.00%	3.00%
Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring [Member]
Fair value	$ 1,381,000	$ 1,299,000