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Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Reserved Shares of Common Stock for Future Issuance

The Company has reserved for future issuance the following number of shares of common stock:

	December 31, 2017		December 31, 2016
Common stock options and RSU's outstanding ⁽¹⁾		4,388,752		3,579,694
Shares available for issuance under the 2014 Plan ⁽²⁾		1,790,600		1,140,328
Warrant to purchase common stock		509,611		—
Shares available for issuance under the ESPP ⁽³⁾		652,290		803,105
Total		7,341,253		5,523,127

⁽¹⁾

Includes awards granted under the 2014 Plan and the 2016 Inducement Award Program.

⁽²⁾

On January 1, 2018, January 1, 2017 and January 1, 2016, the shares reserved for future grants under the 2014 Plan increased by 1,575,329, 1,265,863 and 986,800 shares, respectively, pursuant to the 2014 Plan Evergreen Provision. On December 19, 2017, the Company’s Board of Directors approved 750,000 shares to become available for issuance effective January 1, 2018 under the 2016 Inducement Award Program. As these shares are not available for issuance as of year-end, they have been excluded from the table above.

⁽³⁾

On February 28, 2017 and February 28, 2016, the shares reserved for future issuance under the ESPP increased by 0 and 273,404 shares, respectively, pursuant to the ESPP Evergreen Provision.

Schedule of Assumptions Used in Black-Scholes Option Pricing Model

The assumptions used in the Black-Scholes pricing model to estimate the grant date fair value of options granted to employees are as follows:

	Year ended December 31,
	2017	2016		2015
Risk-free interest rate	1.81% - 2.27%	1.16% - 2.03%		1.44% - 1.95%
Dividend yield	0.00%		0.00%		0.00%
Volatility	78.57% - 85.81%	64.78% - 82.40%		62.47% - 81.25%
Expected term (years)	5.51 - 6.25	5.51 - 6.25		5.51 - 6.25

Schedule of Stock Option Activity

The following table summarizes the Company’s stock option activity for the year ended December 31, 2017:

	Shares			Weighted-Average Exercise Price		Weighted-Average Contractual Life (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2016		3,148,006		$	8.93			$	10,437,947
Granted		1,332,400		$	11.95
Exercised		(291,439	)	$	5.28			$	2,689,563
Forfeited		(528,953	)	$	14.80			$	1,502,894
Expired/cancelled		—
Outstanding, December 31, 2017		3,660,014		$	9.47		8.00	$	21,932,858
Options exercisable, December 31, 2017		1,574,788		$	7.62		6.85	$	12,971,099
Expected to vest, December 31, 2017		2,085,226		$	10.88

Schedule of Restricted Stock Activity

The following table summarizes the Company’s restricted stock activity for the year ended December 31, 2017:

	Shares			Weighted-Average Grant Date Fair Value
Restricted shares as of December 31, 2016		92,972		$	8.08
Granted		—
Vested		(90,566	)	$	8.56
Forfeited		(2,406	)	$	7.42
Restricted shares as of December 31, 2017		-		$	-

Compensation Cost Related to Share-Based Awards

The Company has recognized the following compensation cost related to share-based awards:

	Years ended December 31,
	2017		2016		2015
	(in thousands)
Research and development	$	6,496	$	2,136	$	2,079
General and administrative		5,784		3,689		2,635
Total	$	12,280	$	5,825	$	4,714

Schedule of Compensation Expense by Type of Award

Compensation expense by type of award:

	Years ended December 31,
	2017		2016		2015
	(in thousands)
Stock options	$	6,512	$	4,674	$	3,660
Restricted stock		158		266		909
Restricted stock units		2,021		780		62
Employee stock purchase plan		176		105		83
Warrant		3,413		—		—
Total	$	12,280	$	5,825	$	4,714

Restricted Stock Units

Schedule of Restricted Stock Activity

A following table summarizes the Company’s RSU activity for the year ended December 31, 2017:

	Shares			Weighted-Average Grant Date Fair Value
Unvested balance, December 31, 2016		431,688		$	7.96
Granted		449,900		$	10.34
Vested		(26,000	)	$	7.70
Forfeited		(126,850	)	$	8.96
Outstanding, December 31, 2017		728,738		$	9.26