Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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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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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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Percentage of performance based award payouts.

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Share based compensation by share based payment award, options term.

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Stock-Based Compensation Plans (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	May. 31, 2015	May. 31, 2011	May. 31, 2009	Jan. 31, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 3.0	$ 2.1		$ 5.3	$ 5.9
Allocated Sharebased Compensation Expense Modification Of Performance Measurement			$ 2.1
Weighted average grant date fair value per share of options granted				$ 9.69	$ 11.96
Aggregate intrinsic value of options exercised				$ 1.6	$ 1.0
Two Thousand And Seven Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved for issuance									500,000
Shares additionally approved for issuance							2,860,000	325,000
Two Thousand And Seven Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				3 years
Two Thousand And Seven Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				5 years
Share based payment award options term				7 years
Two Thousand And Fifteen Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved for issuance						5,485,000
Nineteen Ninety Seven Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award options term				10 years
Restricted Stock \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				1 year
Restricted Stock \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				5 years
Ltip Awards \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage Of Performance Based Award Payouts				0.00%
Granted in Two Thousand Fifteen \| Ltip Awards \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage Of Performance Based Award Payouts				150.00%
Granted Prior To Two Thousand Fifteen \| Ltip Awards \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage Of Performance Based Award Payouts				200.00%