Stock-Based Compensation - Schedule of Information Regarding Standard and Market Condition Based Stock Options Outstanding (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Standard Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, Number of Shares	3,486,157	3,227,167	3,155,631	3,267,838
Options vested and expected to vest using estimated forfeiture rates, Number of Shares	3,319,308	2,994,044	3,019,979
Options exercisable, Number of Shares	2,023,024	1,774,546	2,329,987
Options outstanding, Weighted Average Exercise Price	$ 8.30	$ 7.78	$ 6.65	$ 6.61
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price	$ 8.21	$ 7.61	$ 6.67
Options exercisable, Weighted Average Exercise Price	$ 7.18	$ 6.67	$ 6.91
Options outstanding, Weighted Average Remaining Contractual Life (years)	4 years 10 months 6 days	5 years 5 months 16 days	5 years 2 months 27 days
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	4 years 9 months 18 days	5 years 4 months 28 days	5 years 2 months 1 day
Options exercisable, Weighted Average Remaining Contractual Life (years)	4 years 3 months 4 days	4 years 11 months 12 days	4 years 8 months 9 days
Options outstanding, Aggregate Intrinsic Value	$ 6.6	$ 9.9	$ 3.5
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	6.6	9.6	3.4
Options exercisable, Aggregate Intrinsic Value	6.0	7.5	2.5
Market Condition Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, Number of Shares	50,000	0
Options vested and expected to vest using estimated forfeiture rates, Number of Shares	45,430
Options exercisable, Number of Shares	0
Options outstanding, Weighted Average Exercise Price	$ 11.94	$ 0.00
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price	$ 11.94
Options exercisable, Weighted Average Exercise Price	$ 0.00
Options outstanding, Weighted Average Remaining Contractual Life (years)	6 years 1 month 24 days
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	6 years 1 month 24 days
Options exercisable, Weighted Average Remaining Contractual Life (years)	0 years
Options outstanding, Aggregate Intrinsic Value	0
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	0
Options exercisable, Aggregate Intrinsic Value	$ 0

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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- Definition

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iii)

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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