Note 9 - Property, Plant and Equipment and Construction-in-process - Construction-in-process (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Construction-in-process	$ 306,709	$ 248,835
Projects Under Exploration And Development [Member]
Construction-in-process	54,447	62,920	$ 73,431	$ 69,639
Projects Under Exploration And Development [Member] | Up-front Bonus Lease Costs [Member]
Construction-in-process	17,385	26,491	26,618	30,141
Projects Under Exploration And Development [Member] | Exploration And Development Costs [Member]
Construction-in-process	36,359	35,726	45,977	38,220
Projects Under Exploration And Development [Member] | Interest Capitalized [Member]
Construction-in-process	703	703	$ 836	$ 1,278
Projects Under Construction [Member]
Construction-in-process	252,262	185,915
Projects Under Construction [Member] | Up-front Bonus Lease Costs [Member]
Construction-in-process	37,713	27,473
Projects Under Construction [Member] | Interest Capitalized [Member]
Construction-in-process	12,338	7,975
Projects Under Construction [Member] | Drilling And Construction Costs [Member]
Construction-in-process	$ 202,211	$ 150,467