Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Measurements

Schedule of assets measured at fair value on a recurring basis

        Financial assets measured at fair value on a recurring basis at December 31, 2015 and December 31, 2014 are summarized as follows (in thousands):

Description	Balance as of December 31, 2015		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)
Assets:
Cash equivalents:
Money market funds and overnight repurchase agreements	$	54,077	$	30,077	$	24,000	$	—
Marketable securities:
U.S. government-sponsored enterprise securities		24,290		—		24,290		—
Corporate debt securities		73,651		—		73,651		—
Commercial paper obligations		125,805		—		125,805		—
Asset-backed securities		64,837		—		64,837		—
Total	$	342,660	$	30,077	$	312,583	$	—

Description	Balance as of December 31, 2014		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)
Assets:
Cash equivalents:
Money market funds	$	55,283	$	55,283	$	—	$	—
Corporate debt securities		980		—		980		—
Marketable securities:
Corporate debt securities		70,668		—		70,668		—
Commercial paper obligations		15,250		—		15,250		—
Foreign government bonds		18,520		—		18,520		—
Asset-backed securities		25,742		—		25,742		—
Total	$	186,443	$	55,283	$	131,160	$	—