Face amount or stated value per share of common stock.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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-Glossary Financing Activities

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The noncash expense that represents the cost of restricted stock or unit distributed to employees as compensation.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of additional shares authorized for issuance under an established share-based compensation plan.

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No definition available.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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The noncash expense that accounts for the value of stock or unit options distributed to employees as compensation.

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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			0 Months Ended	12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2014 GBP (£)	Dec. 31, 2013 GBP (£)	Dec. 31, 2014 Stock Options Granted Prior to June 30, 2009	Dec. 31, 2014 Stock Options Granted after June 30, 2009	Dec. 31, 2014 Stock Incentive Plan 2011	Jan. 08, 2014 Stock Incentive Plan 2011 Stock Options	Dec. 31, 2014 Stock Incentive Plan 2011 Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, par value				£ 0.50	£ 0.50
Newly authorized Shares available for award								3.5
Stock options, Vesting Period						3 years	4 years	4 years	4 years
Expire period										10 years
Weighted average fair value of the stock options granted	$ 1.58	$ 6.18	$ 8.79
Cash received from the exercise of options	$ 307,000	$ 627,000	$ 8,205,000
Intrinsic value of options exercised	200,000	2,400,000
Unrecognized stock-based compensation expense related to unvested stock option	9,400,000	15,700,000
Unrecognized stock-based compensation expense related to unvested stock option, recognition period	2 years 4 months 24 days
(Provision) benefits in the consolidated statement of cash flows relating to excess tax benefits	(2,299,000)	(361,000)	11,334,000
Compensation expense related to stock option	7,700,000us-gaap_StockOptionPlanExpense	14,300,000us-gaap_StockOptionPlanExpense	16,700,000us-gaap_StockOptionPlanExpense
Compensation expense in relation to restricted stock units	$ 1,400,000us-gaap_RestrictedStockExpense	$ 400,000us-gaap_RestrictedStockExpense	$ 1,400,000us-gaap_RestrictedStockExpense