Face amount or stated value per share of common stock.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
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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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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (j)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Name Accounting Standards Codification
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 28
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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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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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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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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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) $ / shares in Units, $ in Thousands			12 Months Ended
	Feb. 01, 2016	Jan. 29, 2015	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares	Dec. 31, 2016 £ / shares	Dec. 31, 2015 £ / shares	Mar. 05, 2015 £ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, par value \| £ / shares						£ 0.50	£ 0.50	£ 0.50
Weighted average fair value of the stock options granted \| $ / shares			$ 1.62	$ 2.16	$ 1.58
Grant date fair value of options vested			$ 6,500	$ 9,100	$ 8,100
Proceeds from the exercise of options			287	31	307
Intrinsic value of options exercised			200	6	200
Unrecognized stock-based compensation expense related to unvested stock option			$ 11,800
Unrecognized stock-based compensation expense related to unvested stock option, recognition period			2 years 6 months
Compensation expense related to stock option			$ 6,600	7,900	7,700
Compensation expense in relation to restricted stock units			$ 7,000	$ 6,000	$ 1,400
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock options, Vesting Period			4 years
Stock Incentive Plan 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Newly authorized Shares available for award \| shares			31,500,000
Stock Incentive Plan 2011 \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock options, Vesting Period	4 years	4 years	4 years
Expire period			10 years