Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Summary of Significant Accounting Policies (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Fair Value Measurements
Transfer from Level 1 to Level 2, assets	$ 0		$ 0
Transfer from Level 2 to Level 1, assets	0		0
Other-than-temporary impairment	0	$ 0	0	$ 0
Recurring
Fair Value Measurements
Assets fair value	369,223		369,223		$ 186,443
Recurring \| Money Market Funds and Overnight Repurchase Agreement
Fair Value Measurements
Assets fair value	64,341		64,341		55,283
Recurring \| Corporate debt securities
Fair Value Measurements
Assets fair value					980
Recurring \| Corporate debt securities
Fair Value Measurements
Assets fair value	102,034		102,034		70,668
Recurring \| Commercial paper obligations
Fair Value Measurements
Assets fair value	145,345		145,345		15,250
Recurring \| Foreign government bonds
Fair Value Measurements
Assets fair value					18,520
Recurring \| Asset-backed securities
Fair Value Measurements
Assets fair value	57,503		57,503		25,742
Recurring \| Quoted Prices in Active Markets (Level 1)
Fair Value Measurements
Assets fair value	48,341		48,341		55,283
Recurring \| Quoted Prices in Active Markets (Level 1) \| Money Market Funds and Overnight Repurchase Agreement
Fair Value Measurements
Assets fair value	48,341		48,341		55,283
Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value Measurements
Assets fair value	320,882		320,882		131,160
Recurring \| Significant Other Observable Inputs (Level 2) \| Money Market Funds and Overnight Repurchase Agreement
Fair Value Measurements
Assets fair value	16,000		16,000
Recurring \| Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Fair Value Measurements
Assets fair value					980
Recurring \| Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Fair Value Measurements
Assets fair value	102,034		102,034		70,668
Recurring \| Significant Other Observable Inputs (Level 2) \| Commercial paper obligations
Fair Value Measurements
Assets fair value	145,345		145,345		15,250
Recurring \| Significant Other Observable Inputs (Level 2) \| Foreign government bonds
Fair Value Measurements
Assets fair value					18,520
Recurring \| Significant Other Observable Inputs (Level 2) \| Asset-backed securities
Fair Value Measurements
Assets fair value	$ 57,503		$ 57,503		$ 25,742