Note 2 - Revision of Previously Issued Financial Statements for Immaterial Misstatements (Details Textual) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Depreciation, Depletion and Amortization, Total		$ 46,957	$ 39,779	$ 92,861	$ 79,598	$ 139,800	$ 120,076	$ 155,006	$ 196,408	$ 138,681
Revision of Prior Period, Adjustment [Member]
Depreciation, Depletion and Amortization, Total		$ (2,589)	$ (1,851)	$ (5,260)	$ (4,587)		$ (6,835)	$ (9,020)	$ (8,067)	$ (2,224)
Revision of Prior Period, Adjustment [Member] | Hecla Quebec. Inc [Member]
Depreciation, Depletion and Amortization, Total	$ 38,200