Stock-Based Compensation - Classification of Stock-Based Compensation Expense Narrative (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014 vesting_type	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of award vesting types	3
Weighted-average grant date fair value of options issued	$ 7.02	$ 6.83	$ 7.45
Total intrinsic value of options exercised	$ 2.4	$ 3.9	$ 1.2
Market-based awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	8 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	22,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures and Expirations	155,000	554,000	6,000
Stock-based compensation expense	0	0.2	0.4
Stock-based compensation, maximum number of unvested shares	226,000
Performance-based awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	7,000	0	14,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures and Expirations	16,000	398,000	6,000
Stock-based compensation expense	0.1	0	0.2
Stock-based compensation, maximum number of unvested shares	462,000
Options issued	8,000	67,000	180,000
Total unrecognized compensation cost related to non-vested stock options granted	0.5
Total unrecognized compensation cost, weighted-average period for recognition	3 years 2 months 12 days
Service-based awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures and Expirations	8,000	14,000	1,000
Stock-based compensation expense	0.3	0.5	0.7
Options issued	23,000	52,000	113,000
Expiration term	8 years
Service Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to non-vested stock options granted	0.6
Total unrecognized compensation cost, weighted-average period for recognition	2 years 7 months 12 days
Performance Stock Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options issued	119,000	83,000	90,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Options issued	59,000	28,000	30,000
Percentage of shares vesting on the first anniversary of grant	25.00%
Percentage of shares vesting after the first anniversary of grant	75.00%
Deferred Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options issued	46,000	48,000	25,000
Percentage of shares vested in lieu of directors fees at the grant date	100.00%
Portion of Director fees matched to deferred stock units	25.00%
Vesting period of deferred stock	1 year
Deferred stock units, performance-based stock units and restricted stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	78,000	67,000
Stock-based compensation expense	1.5	1.1	0.7
Total unrecognized compensation cost related to non-vested stock options granted	4.1
Granted to restricted shares to members of its advisory boards	231,000	167,000
Total fair value of stock-based compensation vested	1.4	1.1	0.9
Non Employees [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 0.1
Granted to restricted shares to members of its advisory boards	8,000	8,000	5,000

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Percentage of shares vested in lieu of directors fees at the grant date.

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Share based compensation arrangement by share based payment award equity instruments maximum number of unvested shares.

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Share based compensation arrangement by share based payment award expiration term.

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Share Based Compensation Arrangement By Share Based Payment Award Percentage Of Award Vested After One Year

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The amount of expense, net of income tax, 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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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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Unrecognized cost of unvested options awarded 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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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Number of shares under non-option equity instrument agreements that were either cancelled or expired.

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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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Number of share instruments newly issued under a share-based compensation plan.

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