Summary of Changes to Restructuring Accrual (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Beginning Balance		$ 7,681	$ 7,681
Restructuring charges	$ 21,200		31,783
Cash payments / adjustments			(8,620)
Ending Balance	30,844		30,844	$ 7,681
Employee severance & termination benefits
Restructuring Cost and Reserve [Line Items]
Beginning Balance		4,379	4,379
Restructuring charges	15,500	10,500	31,664	13,300	$ 96,300
Cash payments / adjustments			(7,794)
Ending Balance	28,249		28,249	4,379
Contractual obligations and other
Restructuring Cost and Reserve [Line Items]
Beginning Balance		$ 3,302	3,302
Restructuring charges			119	5,700
Cash payments / adjustments			(826)
Ending Balance	$ 2,595		$ 2,595	$ 3,302