Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities Measured on Recurring Basis

The following table sets forth the fair value of our financial assets and liabilities (excluding restricted cash) allocated into Level 1 and Level 2 that were measured on a recurring basis (in thousands): 

		June 30, 2019									December 31, 2018
									Estimated									Estimated
	Fair Value	Amortized		Unrealized		Unrealized			Fair		Amortized		Unrealized		Unrealized			Fair
	Hierarchy	Cost		Gain		(Loss)			Value		Cost		Gain		(Loss)			Value
Money market funds	Level 1	$	36,826	$	—	$	—		$	36,826	$	19,500	$	—	$	—		$	19,500
Corporate notes and commercial paper	Level 2		127,459		3		(25	)		127,437		166,363		1		(205	)		166,159
U.S. Treasury bills and government agency securities	Level 2		65,168		25		—			65,193		110,270		1		(81	)		110,190
		$	229,453	$	28	$	(25	)	$	229,456	$	296,133	$	2	$	(286	)	$	295,849
Classified as:
Cash equivalents									$	140,903								$	117,836
Short-term investments										88,553									178,013
Total cash equivalents and investments									$	229,456								$	295,849

Summary of Changes in Estimated Fair Value

The following table sets forth a summary of the changes in the estimated fair value of our embedded derivative liabilities and Lonza award during the six-month period ended June 30, 2019 (in thousands):

	Embedded derivative liabilities			Lonza award			Total
Balance as of December 31, 2018	$	2,497		$	9,201		$	11,698
Net change in the fair value		(2,902	)		5,824			2,922
Addition of derivative related to 2019 Secured Term Loan		2,372			—			2,372
Settlement of Lonza award		—			(15,025	)		(15,025	)
Balance as of June 30, 2019	$	1,967		$	—		$	1,967