Note 16 - Employee Benefit Plans (Details Textual)	12 Months Ended
	Dec. 31, 2019 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)
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		$ 2,600,000	$ 2,200,000	$ 2,000,000.0
Defined Contribution Plan, Shares, Held in Employee Stock Ownership and Profit Sharing Plan | shares	508,000	508,000	568,000
Deferred Compensation Arrangement with Individual, Contributions by Employer		$ 241,000	$ 250,000	$ 232,000
Deferred Compensation Arrangement with Individual, Recorded Liability	$ 10,100,000	10,100,000	$ 8,600,000
Defined Benefit Plan, Number of Employees Covered			3
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	$ 2,300,000	$ 2,300,000	$ 2,100,000