Summary of Significant Accounting Policies - Risks and Uncertainties and Use of Estimates (Details)	12 Months Ended
	Dec. 31, 2018 employee customer	Dec. 31, 2017 customer	Dec. 31, 2016 customer
Segment Reporting Information [Line Items]
Number of employees	8,800
Percent of employees located outside of the U.S.	15.00%
Percent of employees covered by collective bargaining agreements	40.00%
USW with Collective Bargaining Arrangements Ratified in 2018 [Member]
Segment Reporting Information [Line Items]
Number of employees	900
Sales Revenue [Member]
Segment Reporting Information [Line Items]
Number of customers | customer	0	0	0