Accounting Policies (Impacts of ASUs) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash used in investing activities	$ 7,472		$ (103,952)	$ (130,638)
Cost of sales	470,319		1,925,202	1,839,993
Selling, general and administrative expenses	23,193		100,300	87,952
Other operating income, net	(5,340)		$ (20,611)	(30,241)
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash used in investing activities	17,984			(59,802)
Cost of sales	470,644			1,843,093
Selling, general and administrative expenses	22,836			86,821
Other operating income, net	(5,340)			(30,270)
Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash used in investing activities	10,512			70,836
Cost of sales	(325)			(3,100)
Selling, general and administrative expenses	357			1,131
Other operating income, net	$ 0			$ 29
Predecessor
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash used in investing activities		$ (845)
Cost of sales		1,262,174
Selling, general and administrative expenses		59,918
Other operating income, net		(15,257)
Predecessor | Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash used in investing activities		15,134
Cost of sales		1,264,464
Selling, general and administrative expenses		59,343
Other operating income, net		(15,257)
Predecessor | Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash used in investing activities		15,979
Cost of sales		(2,290)
Selling, general and administrative expenses		575
Other operating income, net		$ 0