Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

Summary of Fair Value Assumptions for Stock Options

The following table summarizes the Company’s grant date fair value and assumptions used in determining the fair value of all stock options granted:



	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2016	2017	2016
Volatility	72%-73%	75%-76%	72%-74%	75%-77%
Risk-free interest rate	1.73%-1.93%	1.00%-1.18%	1.73%-1.99%	1.00%-1.73%
Dividend yield	0.0%	0.0%	0.0%	0.0%
Expected option term (in years)	6.25	6.25	6.25	6.25
Weighted average fair value of stock options granted	$9.59	$7.79	$10.18	$8.74

Summary of Stock Option Activity

The following table summarizes the Company’s aggregate stock option activity for the nine months ended September 30, 2017:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life in Years	Aggregate Intrinsic Value (in thousands)
Options outstanding at December 31, 2016	7,116,706		$	13.30
Granted	2,207,390		$	15.42
Exercised	(336,135	)	$	8.78
Forfeited or expired	(386,668	)	$	15.59
Options outstanding at September 30, 2017	8,601,293		$	13.92	7.65	$	148,771
Vested and expected to vest at September 30, 2017	8,269,230		$	13.88	7.60	$	143,327
Exercisable at September 30, 2017	3,904,073		$	12.46	6.40	$	73,193

Summary of Exercise Price and Number of Stock Options Exercisable

The following table summarizes the range of exercise prices and the number of stock options outstanding and exercisable:



Outstanding as of September 30, 2017					Exercisable as of September 30, 2017
Range of Exercise Prices ($)		Number of Options	Weighted Average Remaining Contractual Term (in years)	Weighted Average Exercise Price ($)	Number of Options	Weighted Average Exercise Price ($)
3.03	4.55	988,195	4.89	3.59	988,195	3.59
6.90	6.90	137,577	5.47	6.90	100,077	6.90
6.96	10.85	1,081,121	8.55	10.76	289,330	10.52
11.14	12.58	1,095,757	6.65	12.17	735,792	12.16
12.66	13.58	185,880	7.76	13.24	89,704	13.29
13.67	13.67	865,660	9.27	13.67	—	—
13.94	15.91	862,300	8.01	14.97	339,372	14.55
16.07	16.16	1,009,781	7.93	16.13	463,410	16.12
16.19	17.16	871,266	9.34	17.10	31,741	16.30
17.24	27.38	1,503,756	7.41	21.20	866,452	21.13

Summary of RSU Activity

The following table summarizes the Company’s RSU award activity during the nine months ended September 30, 2017:



	Number of RSUs		Weighted Average Grant Price ($)
Outstanding at December 31, 2016	89,194		10.85
Granted	46,914		17.16
Released	(89,194	)	(10.85	)
Outstanding at September 30, 2017	46,914		17.16

Summary of Allocation of Employee Stock-Based Compensation

The following table summarizes the aggregate stock-based compensation recorded in the Consolidated Statements of Comprehensive Loss related to stock options and RSUs during the three and nine months ended September 30, 2017 and 2016:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(in millions)
Research and development expenses	$	1.8	$	1.7	$	4.8	$	4.6
General and administrative expenses	2.9		3.4		8.5		9.3
Total	$	4.7	$	5.1	$	13.3	$	13.9