Income taxes - Net Deferred Tax Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
U.S. net operating loss carryforwards	$ 33,767	$ 11,010
Foreign net operating loss carryforwards	899	659
Tax credit carryforwards	23,274	3,638
Capitalized research and development expenses, net	1,372	1,837
Deferred revenue	12,050us-gaap_DeferredTaxAssetsDeferredIncome	21,830us-gaap_DeferredTaxAssetsDeferredIncome
Accruals and other	7,552	4,177
Total deferred tax assets	78,914us-gaap_DeferredTaxAssetsGross	43,151us-gaap_DeferredTaxAssetsGross
Intangible assets	(11,084)
Fixed assets	(2,526)	(2,596)
Less valuation allowance	$ (65,304)	$ (40,555)

Deferred tax assets capitalized research and development expenses.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from deferred income.

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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 before allocation of valuation allowances of deferred tax asset attributable to deductible domestic operating loss carryforwards. Excludes state and local operating loss carryforwards.

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

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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 reserves and accruals.

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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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Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.

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