Acquisitions (Details) - USD ($) $ in Thousands			3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 01, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
Inventories		$ 450,263	$ 610,212		$ 610,212		$ 450,263
Gain (loss) on acquisition					6,025	$ 0
Acquisition and integration related costs			0	$ 6,749	0	44,337
Jiangxi Jiangli New Materials Science and Technology Co. Ltd.
Business Acquisition [Line Items]
Total purchase price		145,000
Property, plant and equipment		29,000					29,000
Other intangibles		32,000					32,000
Deferred tax liabilities		3,700					3,700
Fair value of net working capital		$ 6,200					6,200
Inventories			37,100		37,100
Inventory markup			23,100		23,100
Acquired finite-lived intangible assets, weighted average useful life		17 years
Sales de Magnesio Ltda.
Business Acquisition [Line Items]
Total purchase price	$ 8,300
Percentage of equity interests acquired	50.00%
Rockwood Holdings, Inc.
Business Acquisition [Line Items]
Acquisition and integration related costs				6,300		42,400
Other significant projects
Business Acquisition [Line Items]
Acquisition and integration related costs				$ 400		$ 1,900
Lithium and Advanced Materials | Jiangxi Jiangli New Materials Science and Technology Co. Ltd.
Business Acquisition [Line Items]
Goodwill							$ 87,700
Patents and technology | Jiangxi Jiangli New Materials Science and Technology Co. Ltd.
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, weighted average useful life		20 years
Customer lists and relationships | Jiangxi Jiangli New Materials Science and Technology Co. Ltd.
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, weighted average useful life		18 years
Other | Jiangxi Jiangli New Materials Science and Technology Co. Ltd.
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, weighted average useful life		3 years
Cost of goods sold
Business Acquisition [Line Items]
Acquisition and integration related costs			1,800		12,500
Cost of goods sold | Jiangxi Jiangli New Materials Science and Technology Co. Ltd.
Business Acquisition [Line Items]
Utilization of inventory markup			600		23,100
Other (expenses) income, net | Sales de Magnesio Ltda.
Business Acquisition [Line Items]
Gain (loss) on acquisition			(1,400)		6,000
Selling, general and administrative expenses
Business Acquisition [Line Items]
Acquisition and integration related costs			$ 3,800		$ 13,900