Note 3 - Balance Sheet Details - Selected Balance Sheet Items (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts receivable:
Trade receivables	$ 79,829	$ 82,521
Other receivables	1,478	1,456
Total accounts receivable, less allowances of $10,803 and $8,538	81,307	83,977
Inventories:
Finished goods	157,348	175,074
Work in process	1,183	1,363
Raw materials	4,008	4,026
Repair parts	10,254	10,116
Operating supplies	2,004	1,524
Total inventories, less loss provisions of $7,750 and $9,453	174,797	192,103
Accrued liabilities:
Accrued incentives	24,337	19,359
Other accrued liabilities	26,320	24,369
Total accrued liabilities	$ 50,657	$ 43,728