Share-Based Compensation

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement [Abstract]

The Company's Equity Incentive Plans consist of the Amended and Restated 2007 Equity Incentive Plan (the "Plan") and the 2007 Director Option Plan (the "2007 Director Plan"). The Plan provides for the granting of restricted stock units and options to purchase common stock in the Company to employees, directors, advisors, and consultants at a price to be determined by the Company's Board of Directors. The Plan is intended to encourage ownership of stock by employees and consultants of the Company and to provide additional incentives for them to promote the success of the Company's business. The 2007 Director Plan is intended to promote the recruiting and retention of highly qualified eligible directors and strengthen the commonality of interest between directors and stockholders by encouraging ownership of common stock of the Company. The Board of Directors, or its committee, is responsible for determining the individuals to be granted options, the number of options each individual will receive, the option price per share, and the exercise period of each option.

Stock Option Grants

The fair value of the stock options granted is estimated on the date of grant using a Black-Scholes option pricing model with the following weighted-average assumptions:



		Three Months Ended September 30,						Nine Months Ended September 30,
		2019			2018			2019			2018
Expected stock price volatility		73.6		%	75.5		%	74.1		%	80.7		%
Risk free interest rate		1.6		%	2.7		%	2.4		%	2.4		%
Expected life of options (years)	⁽¹⁾	5.68			5.62			5.68			5.62
Expected annual dividend per share		$	—		$	—		$	—		$	—

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⁽¹⁾ The average expected life is determined using actual historical data.

A summary of the Company's stock options for the nine months ended September 30, 2019 were as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Options outstanding, December 31, 2018	15,810		$	8.63
Granted	3,913		$	10.37
Exercised	(1,353	)	$	5.77
Forfeited	(701	)	$	11.05
Expired	(139	)	$	14.00
Options outstanding, September 30, 2019	17,530		$	9.10	6.5 years	$	19.5
Vested and unvested expected to vest, September 30, 2019	16,792		$	9.02	6.4 years	$	19.4
Exercisable at September 30, 2019	10,896		$	8.22	5.2 years	$	16.9

As of September 30, 2019, the total unrecognized compensation cost related to non-vested stock options granted was $36.5 million and is expected to be recognized over a weighted average period of three years.

Restricted Stock Units and Performance-Based Restricted Stock Units (collectively "RSUs")

RSUs awarded under the Plan are generally subject to graded vesting and are contingent on an employee's continued service. RSUs are generally subject to forfeiture if employment terminates prior to the release of vesting restrictions. The Company expenses the cost of the RSUs, which is determined to be the fair market value of the shares of common stock underlying the RSUs at the date of grant, ratably over the period during which the vesting restrictions lapse. A summary of non-vested RSU activity under the Plan for the nine months ended September 30, 2019 is as follows:



	Number of Shares		Weighted Average Grant Date Fair Value		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Non-vested units as of December 31, 2018	3,712		$	10.59
Granted	3,412		$	10.99
Vested	(835	)	$	9.43
Forfeited	(449	)	$	10.47
Non-vested units as of September 30, 2019	5,840		$	11.06	2.5 years	$	46.8

All non-vested units granted as of September 30, 2019 are expected to vest over their normal term. As of September 30, 2019, there was $43.1 million of total unrecognized compensation cost related to unvested RSUs with service-based vesting conditions. These costs are expected to be recognized over a weighted average period of three years.

Compensation Expense Related to Equity Awards

The following table summarizes information related to compensation expense recognized in the Consolidated Statements of Operations related to the equity awards:



	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2019		2018		2019		2018
Equity compensation expense recognized in:
Research and development expense	$	3,106	$	2,905	$	12,090	$	8,603
Selling, general, and administrative expense	5,737		4,149		19,432		12,270
Total equity compensation expense	$	8,843	$	7,054	$	31,522	$	20,873