Income Taxes - Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate (Detail)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Federal statutory income tax rate	[1]	19.30%	20.00%	20.30%
Tax effect of international operations		(11.30%)	(11.80%)	(6.50%)
Change in valuation allowances		8.00%	9.70%	6.90%
Withholding taxes		0.40%	0.90%	0.60%
Interest limitations		0.60%	0.60%	0.70%
Non-deductible transaction costs		0.70%	0.10%	0.50%
Effective tax rate		1.90%	19.50%	22.50%
Effective Income Tax Rate Reconciliation, Deduction, Amount		(1.70%)	0.00%	0.00%
Effective Income Tax Rate Reconciliation Tax Effect of US Tax Reform		(17.30%)	0.00%	0.00%
Effective Income Tax Rate Reconciliation Tax Effect of Early Extinguishment of Debt		3.20%	0.00%	0.00%

[1] The statutory rate for 2017, 2016 and 2015 reflects the U.K. statutory rate of 19.3%, 20.0% and 20.3%, respectively.