Reconciliation of income tax computed at US Federal tax rates (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Abstract]
Statutory Income Tax	35.00%	35.00%	35.00%
Foreign Rate Differential, Inclusive of Foreign Rate Changes	(1.10%)	(2.20%)	(2.50%)
U.S. Deferred Tax Liability Remeasurement	(7.00%)	0.00%	0.00%
Deemed Repatriation Tax on Foreign Earnings and Profit (E&P)	4.70%	0.00%	0.00%
Tax Credits	(1.50%)	(1.60%)	(1.40%)
Other Items, Net	(0.90%)	(0.30%)	(1.10%)
Effective Tax	29.20%	30.90%	30.00%