Income Taxes - Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate Additional Information (Detail)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Federal statutory income tax rate	[1]	20.00%	20.30%	21.00%

[1] The statutory rate for 2016, 2015 and 2014 reflects the U.K. statutory rate of 20.0 percent, 20.3 percent and 21.0 percent, respectively.