GRT Acquisition - Estimated Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	16 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 01, 2016
Assets
Goodwill	$ 56,056	$ 54,613
GRT Acquisition
Assets
Cash	8,091		$ 8,091
Accounts receivable	2,844		2,844
Notes receivable	3,050		3,050
Inventory	8,468		7,983
Other current assets	981		981
Property, plant & equipment	47,541		46,712
Intangible assets	7,428		7,412
Other long-term assets	289		289
Goodwill	33,250		33,861
Liabilities
Accounts payable	(62,289)		(61,570)
Notes payable	(10,122)		(10,122)
Accrued liabilities	(2,866)		(2,866)
Long-term debt	(3,383)		(3,383)
Other long-term liabilities	(940)		(940)
Net assets and liabilities assumed	32,342		32,342
Noncontrolling shareholder interest	(18,323)		(18,323)
Cooper Tire & Rubber Company consideration	14,019		$ 14,019
Adjustments
Inventory	485
Property, plant & equipment	829
Intangible assets	16
Goodwill	(611)
Accounts payable	$ (719)