Income Taxes - Deferred Tax Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Summary Of Net Deferred Tax Assets [Line Items]
Net operating loss carryforwards	$ 132.2	$ 132.8
Capitalized research and development expenses	5.0	7.2
Tax credits	9.0	7.3
Share-based compensation	15.5	12.2
Fixed and intangible assets	1.2	1.1
Other, net	7.0us-gaap_DeferredTaxAssetsOther	5.4us-gaap_DeferredTaxAssetsOther
Total gross deferred tax assets	169.9us-gaap_DeferredTaxAssetsGross	166.0us-gaap_DeferredTaxAssetsGross
Less: valuation allowance	(169.0)	(164.7)
Deferred tax liability related to acquired intangibles assets	(1.0)	(1.4)
Net deferred tax asset (liability)	$ (0.1)us-gaap_DeferredTaxAssetsNet	$ (0.1)us-gaap_DeferredTaxAssetsNet

Deferred Tax Assets Goodwill And Intangible Assets Intangible Assets

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed.

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The tax effect as of the balance sheet date of the amount of future tax deductions arising from all unused tax credit carryforwards which have been reduced by a valuation allowance.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from other provisions, reserves, allowances, and accruals not separately disclosed.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount of deferred tax liability attributable to taxable temporary differences from intangible assets other than goodwill.

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