Note 15 - Benefit Plans (Details Textual) - USD ($) $ in Millions		12 Months Ended
	Apr. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay		4.25%
Defined Contribution Plan, Cost		$ 1.3	$ 1.2	$ 1.2
Stock Issued During Period, Shares, Employee Stock Purchase Plans		1,351	1,362
Stock Purchase Plan [Member]
Common Stock, Capital Shares Reserved for Future Issuance		250,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		244,000
Maximum [Member]
Interest Expense, Deferred Compensation Plan		$ 0.1	$ 0.1	$ 0.1
Other Liabilities [Member]
Deferred Compensation Liability, Current and Noncurrent		$ 3.2	$ 3.4
Scenario, Forecast [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	5.00%