Balance Sheet Details (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts receivable:
Accounts receivable	$ 100,948	$ 89,997
Allowances for accounts receivable	6,987	9,051
Inventories:
Finished goods	183,560	170,774
Work in process	1,441	1,485
Raw materials	3,994	3,906
Repair parts	10,404	10,240
Operating supplies	1,419	1,481
Total inventories, less loss provisions of $10,120 and $10,308	200,818	187,886
Inventory loss provisions	10,120	10,308
Accrued liabilities:
Accrued incentives	25,075	19,728
Other accrued liabilities	25,390	23,495
Total accrued liabilities	50,465	43,223
Trade receivables
Accounts receivable:
Accounts receivable	99,080	88,786
Other receivables
Accounts receivable:
Accounts receivable	$ 1,868	$ 1,211