Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2017

Summary of Significant Accounting Policies

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

As of June 30, 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 June 30, 2017 (in thousands):

	Fair Value Measurements at June 30, 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	$	131,469	$	131,469	$	—	$	—

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 June 30, 2017 and December 31, 2016 is summarized below (in thousands):

	June 30,		December 31,
	2017		2016
Raw materials	$	124	$	357
Work in process		3,358		1,835
Total	$	3,482	$	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		Six Months Ended
	June 30,		June 30,
	2017	2016	2017	2016
Options outstanding to purchase common stock and unvested restricted stock	15,588	11,919	15,588	11,919
Common stock equivalents under treasury stock method for options	1,224	232	463	297
Shares issuable upon conversion of convertible notes	23,878	23,878	23,878	23,878
Common stock equivalents under if-converted method for convertible notes	23,878	2,886	23,878	1,443

Schedule of assumptions

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Dividend	None		None		None		None
Volatility	68.17	%	64.13	%	67.10	%	64.06	%
Risk-free interest rate	1.90	%	1.40	%	2.01	%	1.46	%
Expected life (years)	6.0		6.3		6.0		6.3

Summary of stock option activity

A summary of option activity under the 2006 and 2016 Plans as of June 30, 2017, and changes during the six 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	1,428	$	2.84
Exercised	(10)		3.30
Forfeited/Canceled	(1,916)	$	10.47
Outstanding at June 30, 2017	13,181	$	9.89

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 June 30, 2017 and changes during the six month period ended June 30, 2017 is presented below (in thousands except weighted-average data):

	Number of
	Restricted
	Stock Shares
Unvested at December 31, 2016	199
Awarded	2,253
Vested	(25)
Forfeited	(20)
Unvested at June 30, 2017	2,407

Schedule of percentage of total revenues recognized from each significant customer

	Three Months Ended				Six Months Ended
	June 30,				June 30,
Collaborative Partner:	2017		2016		2017		2016
Bayer	—	%	—	%	—	%	37	%
CytomX	3	%	10	%	22	%	5	%
Roche	17	%	80	%	21	%	49	%
Sanofi	77	%	—	%	53	%	—	%