Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Significant Accounting Policies

Schedule of inventory

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

	December 31,		December 31,
	2017		2016
Raw materials	$	40	$	357
Work in process		998		1,835
Total	$	1,038	$	2,192

Schedule of components of other accrued liabilities

Other accrued liabilities consisted of the following at December 31, 2017 and 2016 (in thousands):

	December 31,		December 31,
	2017		2016
Accrued contract payments	$	4,901	$	1,980
Accrued clinical trial costs		8,400		4,700
Accrued professional services		723		865
Accrued employee benefits		574		676
Accrued public reporting charges		156		156
Accrued interest on convertible senior notes		—		2,388
Other current accrued liabilities		1,013		385
Total	$	15,767	$	11,150

Schedule of 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, 2017 (in thousands):

	Fair Value Measurements at December 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	$	240,013	$	240,013	$	—	$	—

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 estimated useful lives of property and equipment

Machinery and equipment	5 years
Computer hardware and software	3 years
Furniture and fixtures	5 years
Leasehold improvements	Shorter of remaining lease term or 7 years

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 unvested restricted stock and the if-converted method for the convertible notes, are shown in the following table (in thousands):

	Year Ended December 31,	Six Months Ended December 31,	Year Ended June 30,
	2017	2016	2016	2015
Options outstanding to purchase common stock and unvested restricted stock at end of period	14,290	13,878	11,919	9,739
Common stock equivalents under treasury stock method for options and unvested restricted stock	1,579	1	735	770
Shares issuable upon conversion of convertible notes at end of period	501	23,878	23,878	—
Common stock equivalents under if-converted method for convertible notes	501	23,878	718	—

Schedule of risk-free rate of the stock options based on US Treasury rate

	Year Ended		Six Months  Ended
	December 31,		December 31,		Year Ended June 30,
	2017		2016		2016		2015
Dividend	None		None		None		None
Volatility	67.34	%	65.63	%	66.34	%	60.86	%
Risk-free interest rate	2.00	%	1.29	%	1.80	%	1.84	%
Expected life (years)	6.0		6.3		6.3		6.3

Summary of stock option activity

A summary of option activity under the 2006 and 2016 Plans as of December 31, 2017, December 31, 2016, and June 30, 2016 and changes during the year ended December 31, 2017, the six month period ended December 31, 2016 and the year ended June 30, 2016 is presented below (in thousands, except weighted‑average data):

		Weighted-		Weighted-
	Number	Average		Average	Aggregate
	of Stock	Exercise		Remaining	Intrinsic
	Options	Price		Life in Yrs.	Value
Outstanding at June 30, 2015	9,689	$	12.49
Granted	3,340	$	14.34
Exercised	(555)		9.30
Forfeited/Canceled	(661)		14.84
Outstanding at June 30, 2016	11,813		13.03	6.82	$	—
Outstanding at June 30, 2016—vested or unvested and expected to vest	11,475		13.05	6.76	$	—
Exercisable at June 30, 2016	6,453	$	12.63	5.30		—
Outstanding at June 30, 2016	11,813	$	13.03
Granted	3,536		2.90
Exercised	—		—
Forfeited/Canceled	(1,670)		10.64
Outstanding at December 31, 2016	13,679		10.70	6.55	$	23
Outstanding at December 31, 2016—vested or unvested and expected to vest	13,516		10.76	6.52	$	22
Exercisable at December 31, 2016	7,898	$	13.15	4.70		—
Outstanding at December 31, 2016	13,679	$	10.70
Granted	1,589		3.21
Exercised	(191)		3.42
Forfeited/Canceled	(3,106)		10.33
Outstanding at December 31, 2017	11,971		9.92	6.17	$	13,513
Outstanding at December 31, 2017—vested or unvested and expected to vest	11,881	$	9.96	6.15	$	13,283
Exercisable at December 31, 2017	7,996	$	12.16	4.97	$	3,733

Summary of restricted stock activity

A summary of restricted stock activity under the 2006 and 2016 Plans as of December 31, 2017 and December 31, 2016, and changes during the year ended December 31, 2017, six month period ended December 31, 2016 and the fiscal year ended June 30, 2016 is presented below (in thousands, except weighted‑average data):

	Number of	Weighted-
	Restricted	Average Grant
	Stock Shares	Date Fair Value
Unvested at June 30, 2015	50	$	9.23
Awarded	75		5.65
Vested	(19)		10.13
Unvested at June 30, 2016	106	$	6.54
Awarded	118		3.15
Vested	—		—
Forfeited	(25)		7.52
Unvested at December 31, 2016	199	$	4.41
Awarded	2,253	$	2.71
Vested	(25)		5.87
Forfeited	(108)		2.68
Unvested at December 31, 2017	2,319	$	2.82

Summary of vested stock option activity

A summary of option activity for options vested during the year ended December 31, 2017 and the six months ended December 31, 2016 and fiscal years ended June 30, 2016 and 2015 is presented below (in thousands):

	Year Ended December 31,		Six Months Ended December 31,		Year Ended June 30,
	2017		2016		2016		2015
Total fair value of options vested	$	10,964	$	17,121	$	15,298	$	16,145
Total intrinsic value of options exercised		598		—		3,142		3,275
Cash received for exercise of stock options		650		—		5,161		4,429

Schedule of percentage of total revenues recognized from each significant customer

	Year Ended December 31,		Six Months Ended December 31,		Year Ended June 30,
Collaborative Partner:	2017		2016		2016		2015
Bayer	—	%	—	%	17	%	—	%
CytomX	13	%	—	%	—	%	—	%
Debiopharm	26	%	—	%	—	%	—	%
Lilly	1	%	4	%	11	%	21	%
Novartis	—	%	24	%	1	%	43	%
Roche	24	%	60	%	43	%	23	%
Sanofi	31	%	—	%	—	%	—	%
Takeda	4	%	8	%	16	%	—	%