Labor Union Contracts (Details)	6 Months Ended
	Jun. 30, 2017
Workforce subject to collective bargaining arrangements, expiring remainder of fiscal year
Concentration risk
Number of unionized employees	1,000
Workforce subject to collective bargaining arrangements, effective June 18, 2017
Concentration risk
Number of unionized employees	10,000
Total number of employees | Unionized employees concentration risk
Concentration risk
Concentration risk (percent)	36.00%
Total number of employees | Unionized employees concentration risk | Workforce subject to collective bargaining arrangements, effective June 18, 2017
Concentration risk
Concentration risk (percent)	25.00%