Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2017

Summary of Significant Accounting Policies

Schedule of assets that are required to be measured at fair value on a recurring basis

As of March 31, 2017, the Company held certain assets that are required to be measured at fair value on a recurring basis.  The following table represents the fair value hierarchy for the Company’s financial assets measured at fair value on a recurring basis as of March 31, 2017 (in thousands):

	Fair Value Measurements at March 31, 2017 Using
			Quoted Prices in				Significant
			Active Markets for		Significant Other		Unobservable
			Identical Assets		Observable Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
Cash equivalents	$	108,296	$	108,296	$	—	$	—

As of December 31, 2016, the Company held certain assets that are required to be measured at fair value on a recurring basis. The following table represents the fair value hierarchy for the Company’s financial assets measured at fair value on a recurring basis as of December 31, 2016 (in thousands):

	Fair Value Measurements at December 31, 2016 Using
			Quoted Prices in				Significant
			Active Markets for		Significant Other		Unobservable
			Identical Assets		Observable Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
Cash equivalents	$	144,176	$	144,176	$	—	$	—

Schedule of inventory

Inventory at March 31, 2017  and December 31, 2016 is summarized below (in thousands):

	March 31,		December 31,
	2017		2016
Raw materials	$	125	$	357
Work in process		3,100		1,835
Total	$	3,225	$	2,192

Schedule of common stock equivalents, as calculated in accordance with the treasury-stock method

The Company’s common stock equivalents, as calculated in accordance with the treasury‑stock method for the options and the if-converted method for the convertible notes, are shown in the following table (in thousands):

	Three Months Ended
	March 31,
	2017	2016
Options outstanding to purchase common stock and unvested restricted stock	13,690	11,679
Common stock equivalents under treasury stock method for options	110	361
Shares issuable upon conversion of convertible notes	23,878	—
Common stock equivalents under if-converted method for convertible notes	23,878	—

Schedule of assumptions

	Three Months Ended March 31,
	2017		2016
Dividend	None		None
Volatility	66.89	%	63.90	%
Risk-free interest rate	2.03	%	1.61	%
Expected life (years)	6.0		6.3

Summary of stock option activity

A summary of option activity under the 2006 and 2016 Plans as of March 31, 2017, and changes during the three month period then ended is presented below (in thousands, except weighted-average data):

		Weighted-
	Number	Average
	of Stock	Exercise
	Options	Price
Outstanding at December 31, 2016	13,679	$	10.70
Granted	1,187	$	2.48
Exercised	—
Forfeited/Canceled	(1,176)	$	11.27
Outstanding at March 31, 2017	13,690	$	9.94

Summary of restricted stock activity

A summary of restricted stock activity under the 2006 and 2016 Plans (inclusive of the performance awards noted above) as of March 31, 2017 and changes during the three month period ended March 31, 2017 is presented below (in thousands):

		Weighted-
	Number of	Average
	Restricted	Exercise
	Stock Shares	Price
Unvested at December 31, 2016	199	$	4.41
Awarded	2,014	$	2.47
Vested	(6)	$	6.53
Forfeited	(20)	$	3.15
Unvested at March 31, 2017	2,187	$	2.63

Schedule of percentage of total revenues recognized from each significant customer

	Three Months Ended
	March 31,
Collaborative Partner:	2017		2016
Bayer	—	%	51	%
CytomX	48	%	3	%
Roche	27	%	37	%
Sanofi	21	%	—	%