Balance Sheet Details (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts receivable:
Accounts receivable	$ 89,997	$ 85,113
Allowance for doubtful accounts	9,051	7,832
Inventories:
Finished goods	170,774	152,261
Work in process	1,485	1,625
Raw materials	3,906	4,432
Repair parts	10,240	10,558
Operating supplies	1,481	1,133
Total inventories, less loss provisions of $10,308 and $9,484	187,886	170,009
Inventory loss provision	10,308	9,484
Accrued liabilities:
Accrued incentives	19,728	19,771
Other accrued liabilities	23,495	22,036
Total accrued liabilities	43,223	41,807
Trade receivables
Accounts receivable:
Accounts receivable	88,786	82,851
Other receivables
Accounts receivable:
Accounts receivable	$ 1,211	$ 2,262