Note 2 - Revenues (Details Textual) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contract with Customer, Including Assessed Tax	$ 40,322	$ 54,614	$ 54,926	$ 48,634	$ 49,253	$ 46,138	$ 41,169	$ 41,660	$ 198,496	$ 178,220
Gearing [Member]
Contract with Customer, Asset, after Allowance for Credit Loss, Total	$ 815								815
Transferred over Time [Member]
Revenue from Contract with Customer, Including Assessed Tax									2,253	$ 0
Transferred over Time [Member] | Gearing [Member]
Revenue from Contract with Customer, Including Assessed Tax									$ 1,438