Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred tax asset
Net operating loss carryforward	$ 133,684	$ 99,058
Research and development credit carry forwards	9,911	4,048
Stock based compensation and other	26,510us-gaap_DeferredTaxAssetsOther	9,094us-gaap_DeferredTaxAssetsOther
Total deferred tax assets	170,105us-gaap_DeferredTaxAssetsGross	112,200us-gaap_DeferredTaxAssetsGross
Valuation Allowance	(170,105)	(112,200)
Deferred tax asset, net of allowance	$ 0us-gaap_DeferredTaxAssetsNet	$ 0us-gaap_DeferredTaxAssetsNet

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 temporary differences from in-process research and development costs expensed in connection with a business combination.

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

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