Note 16 - Employee Benefit Plans (Details Textual) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Benefit Plan, Employer Additional Contribution of Stock, Percent	2.00%
Defined Contribution Plan, Cost	$ 2,000	$ 1,900	$ 1,800
Defined Contribution Plan, Shares, Held in Employee Stock Ownership and Profit Sharing Plan	577	567
Deferred Compensation Arrangement with Individual, Contributions by Employer	$ 232	$ 293	$ 171
Deferred Compensation Arrangement with Individual, Recorded Liability	$ 8,200	5,600
Defined Benefit Plan, Number of Employees Covered	3
Defined Benefit Plan, Number of Present Employees Covered	2
Defined Benefit Plan, Number of Retired Employees Covered	1
Deferred Compensation Arrangement with Individual, Requisite Service Period	25 years
Defined Benefit Plan, Accumulated Benefit Obligation	$ 2,200	$ 2,100
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.59%	4.10%