Critical and Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies and Standards Update

Schedule of estimated useful lives of other plant and equipment for computation of depreciation using straight-line method

Buildings and improvements	5 to 25 years
Machinery and equipment	3 to 20 years
Furniture and fixtures	3 years

Exploration costs included in cost of product sold

	2017		2016		2015
Exploration costs	$	985	$	1,179	$	1,778

Accounting Standards Update 2014-09 [Member]

New Accounting Pronouncements Or Change In Accounting Principle [Line Items]

Schedule Of New Accounting Pronouncements And Changes In Accounting Principles [Table Text Block]

	Balance as of December 31, 2017		Adjustment Due to ASC 606		Balance as of January 1, 2018
Assets
Accounts receivable	$	50,075	$	781	$	50,856
Inventories, net		72,904		(660)		72,244
Equity
Retained Earnings	$	347,046	$	121	$	347,167