Note 3 - Income Taxes - Summary of the Difference Between Statutory Federal Income Tax Rate and Effective Rate (Details)		12 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Statutory federal income tax rate	21.00%	24.28%	35.00%	34.00%	34.00%
State franchise taxes (net of federal tax benefit)		5.70%		6.20%	5.20%
Revalue of deferred taxes due to federal rate change		176.00%
Effect of federal rate change on beginning net deferred tax liabilities		(34.00%)
Business meals/gifts/other permanent differences		(0.40%)		(0.80%)	(2.30%)
Domestic production activity deduction and deferred revenue		(0.90%)
Dividends received deduction		5.80%		10.00%	24.50%
Reversal of uncertain and unrecognized tax position				37.60%
Penalties for uncertain and unrecognized tax benefits				2.00%
Prior year true-up		(1.80%)		1.00%	(2.00%)
Foreign tax credits				2.00%	4.00%
Effect of state rate change on beginning balance of deferred tax liabilities		(0.70%)		(0.30%)	1.40%
Others		(1.70%)		(3.00%)	0.20%
Effective tax rate		172.30%		88.70%	65.00%