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Stock Incentive Plans and Stock Based Compensation - Additional Information (Detail)
Share data in Millions, except Per Share data, unless otherwise specified
 12 Months Ended 12 Months Ended
Dec. 31, 2013
USD ($)
Dec. 31, 2012
USD ($)
Dec. 31, 2011
USD ($)
Dec. 31, 2013
GBP (£)
Dec. 31, 2012
GBP (£)
Dec. 31, 2013
Stock Options Granted Prior to June 30, 2009
Dec. 31, 2013
Stock Options Granted after June 30, 2009
Dec. 31, 2013
Stock Based Compensation Expense
USD ($)
Dec. 31, 2012
Stock Based Compensation Expense
USD ($)
Dec. 31, 2013
Stock Incentive Plan 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Common stock, par       £ 0.50 £ 0.50          
Newly authorized Shares available for award                   3.5
Stock options vesting period           3 years 4 years     4 years
Expire period                   10 years
Weighted average fair value of the stock options granted $ 6.18 $ 8.79 $ 8.61              
Cash received from the exercise of options $ 600,000 $ 8,200,000           $ 600,000 $ 8,300,000  
Intrinsic value of options exercised 2,400,000 34,100,000                
Unrecognized stock-based compensation expense related to unvested stock option 15,700,000 41,800,000                
Unrecognized stock-based compensation expense related to unvested stock option, recognition period 2 years 2 months 12 days                  
(Provision) benefits in the consolidated statement of cash flows relating to excess tax benefits (361,000) 11,334,000 4,199,000              
Compensation expense related to stock option 14,300,000 16,700,000 9,200,000              
Compensation expense in relation to restricted stock units $ 400,000 $ 1,400,000 $ 0