Income Taxes - Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate Additional Information (Detail)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Federal statutory income tax rate	[1]	20.30%	21.00%	7.80%
UNITED KINGDOM
Income Taxes [Line Items]
Federal statutory income tax rate		20.00%	21.00%
SWITZERLAND
Income Taxes [Line Items]
Federal statutory income tax rate				7.80%

[1] The statutory rate for 2015 and 2014 reflects the U.K. statutory rate of 20.25 percent and 21 percent, respectively. For 2013, the statutory rate reflects the Swiss statutory rate of 7.8 percent.