Note 11 - Investments in Affiliates (Details Textual) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Assets, Total	$ 2,508,654	$ 2,478,898	$ 2,379,996
Equity Method Investment, Other than Temporary Impairment	9,600
Foreign Affiliates [Member]
Number of Entities		13
Equity Method Investment, Other than Temporary Impairment	9,600
Foreign Affiliates [Member] | Minimum [Member]
Assets, Total		$ 100
Equity Method Investment, Ownership Percentage		25.00%
Foreign Affiliates [Member] | Maximum [Member]
Assets, Total		$ 82,100
Equity Method Investment, Ownership Percentage		50.00%
Real Estate Entities [Member]
Assets, Total	13,200	$ 66,200
Number of Entities		2
Real Estate Entities [Member] | Minimum [Member]
Equity Method Investment, Ownership Percentage		10.00%
Real Estate Entities [Member] | Maximum [Member]
Equity Method Investment, Ownership Percentage		25.00%
Asphalt Terminal Entity [Member]
Assets, Total		$ 35,300
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Assets, Total	$ 286,398	$ 316,040	$ 298,502