Subsequent Events - Narrative (Detail) - Subsequent Event $ in Millions		3 Months Ended
	Apr. 13, 2018 employee	Jun. 30, 2018 USD ($)
Subsequent Event [Line Items]
Labor agreement, duration	5 years
Labor agreement, number of employees	1,300
Defined benefit plan, labor agreement, employees subject to retirement benefit increase	300
Curtailments | $		$ 10