Income Taxes, Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets [Abstract]
Benefit plans			$ 6,293	$ 6,788
Liabilities and reserves			21,085	12,563
Operating loss and credit carryovers	[1]		82,000	65,392
Other			1,126	1,404
Gross deferred tax assets			110,504	86,147
Valuation allowance	[1]		(54,326)	(50,702)
Deferred tax assets			56,178	35,445
Deferred tax liabilities [Abstract]
Property, plant and equipment			(29,869)	(29,372)
Goodwill			(21,744)	(21,372)
Other			(5,192)	(4,488)
Deferred tax liabilities			(56,805)	(55,232)
Net deferred tax liabilities			$ (627)	$ (19,787)
Increase in valuation allowance amount		$ 16,200

[1] In the first quarter of 2019, the Company recognized an increase in its foreign tax credit carryover and corresponding valuation allowance of $16.2 million, related to the finalization of certain tax regulations.