Note 9 - Property, Plant and Equipment and Construction-in-process - Construction-in-process (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Construction in progress	$ 721,483	$ 479,315
Projects Under Exploration and Development [Member]
Construction in progress	50,702	51,528	$ 84,637	$ 70,958
Projects Under Exploration and Development [Member] | Up-front Bonus Lease Costs [Member]
Construction in progress	5,335	5,347	17,018	17,018
Projects Under Exploration and Development [Member] | Exploration and Development Costs [Member]
Construction in progress	44,664	45,478	66,916	53,237
Projects Under Exploration and Development [Member] | Interest Capitalized [Member]
Construction in progress	703	703	$ 703	$ 703
Projects Under Construction [Member]
Construction in progress	670,781	427,787
Projects Under Construction [Member] | Up-front Bonus Lease Costs [Member]
Construction in progress	39,156	39,144
Projects Under Construction [Member] | Interest Capitalized [Member]
Construction in progress	20,072	9,526
Projects Under Construction [Member] | Drilling And Construction Costs [Member]
Construction in progress	$ 611,553	$ 379,117