Jurisdictions the Company Remains Subject to Tax Examinations (Detail)	12 Months Ended
	Dec. 31, 2017
United States | Earliest Tax Year | Federal
Income Taxes [Line Items]
Tax Years	2013
United States | Earliest Tax Year | State
Income Taxes [Line Items]
Tax Years	2012
United States | Latest Tax Year | Federal
Income Taxes [Line Items]
Tax Years	2017
United States | Latest Tax Year | State
Income Taxes [Line Items]
Tax Years	2017
Ireland | Earliest Tax Year
Income Taxes [Line Items]
Tax Years	2013
Ireland | Latest Tax Year
Income Taxes [Line Items]
Tax Years	2017
United Kingdom | Earliest Tax Year
Income Taxes [Line Items]
Tax Years	2016
United Kingdom | Latest Tax Year
Income Taxes [Line Items]
Tax Years	2017