Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2016

Fair Value Measurements

Assets and liabilities measured at fair value on a recurring basis

Assets and liabilities measured at fair value on a recurring basis as of December 31, 2016 and 2015 are as follows:

			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
			Identical Assets		Inputs		Inputs
Assets	Total		(Level 1)		(Level 2)		(Level 3)
	(in thousands)
December 31, 2016
Money market funds included in cash and cash equivalents	$	36,003	$	36,003	$	—	$	—
Marketable securities:
U.S. Treasury notes		130,173		130,173		—		—
U.S. Government agency securities		7,604		—		7,604		—
Equity securities		1,360		1,360		—		—
Total marketable securities	$	139,137	$	131,533	$	7,604	$	—
Warrants to purchase equity securities		792		—		792		—
Total	$	175,932	$	167,536	$	8,396	$	—
December 31, 2015
Money market funds included in cash and cash equivalents	$	29,601	$	29,601	$	—	$	—
Marketable securities:
U.S. Treasury notes		157,981		157,981		—		—
U.S. Government agency securities		35,055		—		35,055		—
Total	$	222,637	$	187,582	$	35,055	$	—

Assumptions

The assumptions utilized to value the warrants to purchase equity securities on the acquisition date, September 2, 2016 and as of December 31, 2016 are as follows:

	As of September 2,		As of December 31,
	2016		2016
Risk-free interest rate	1.2	%	1.8	%
Expected dividend yield	—	%	—	%
Expected term (in years)	5.0		4.7
Expected volatility	92.3	%	97.5	%