Share based Compensation

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

The Company’s Equity Incentive Plans consist of the Plan and 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.

On December 21, 2018, the Board of Directors of the Company approved an amendment (the "Amendment") to the Plan. The Amendment provides for certain benefits to qualifying Plan Participants who separate from service with the Company due to death, disability or "Retirement" (as such term is defined under the Plan) ("Qualified Participants"). Options granted under the Plan ("Options") to a Qualified Participant shall continue to vest until the 2nd anniversary of the Qualified Participant’s separation and all vested Options held by such Qualified Participant shall remain exercisable until the earlier of the 4th anniversary of the Qualified Participant’s separation or the original expiration date of the Option. Options that are not exercised during this exercise period shall be forfeited. Time-based restricted stock units and restricted stock granted to a Qualified Participant under the Plan that was scheduled to vest within the two year period following the Qualified Participant's separation shall accelerate and be delivered upon such separation. Any time-based restricted stock units or restricted stock that would have vested after such two year period will be forfeited upon the Qualified Participant's separation. Also, per the Amendment, any performance-based restricted stock units under the Plan ("PRSUs") received by the Qualified Participant, shall remain eligible to vest after the Qualified Participant’s separation based on the actual performance of the Company through the end of the performance period applicable to any such PRSU.

Stock Option Grants

The Company uses the fair value method of measuring stock-based compensation, using the fair value of each equity award granted. The Company chose the ‘‘straight-line’’ attribution method for allocating compensation costs and recognized the fair value of each stock option on a straight-line basis over the vesting period of the related awards.

The Company uses the Black-Scholes option pricing model when estimating the grant date fair value for stock-based awards. Use of a valuation model requires management to make certain assumptions with respect to selected model inputs. Expected volatility was based on our historical volatility since our initial public offering in May 2007. Beginning in the third quarter of 2017, the average expected life is determined using our actual historical data versus a ‘‘simplified’’ method used in prior quarters. The ‘‘simplified’’ method of estimating the Company did not have sufficient reliable exercise data to justify a change from the use of the ‘‘simplified’’ method of estimating the expected exercise term of employee stock option grants. The impact from this change was not material. The risk-free interest rate is based on U.S. Treasury, zero-coupon issues with a remaining term equal to the expected life assumed at the date of grant. Forfeitures are estimated based on voluntary termination behavior, as well as a historical analysis of actual option forfeitures.

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:



	Years Ended December 31,
	2019			2018			2017
Expected stock price volatility	74.1		%	78.6		%	82.8		%
Risk free interest rate	2.4		%	2.4		%	2.0		%
Expected life of options (years) ⁽¹⁾	5.68			5.62			6.18
Expected annual dividend per share	$	0.00		$	0.00		$	0.00

______________________________________

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

The weighted average grant-date fair value per share of options granted during 2019, 2018, and 2017 were $6.67, $10.19, and $5.09, respectively.

A summary of the Company's stock options for the year ended December 31, 2019 were as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Options outstanding, December 31, 2016	15,497.5		$	7.37
Granted	3,695.3		$	7.17
Exercised	(2,878.7	)	$	5.67
Forfeited	(1,133.0	)	$	9.55
Options outstanding, December 31, 2017	15,181.1		$	7.48
Granted	2,348.0		$	14.96
Exercised	(1,398.0	)	$	6.54
Forfeited	(313.1	)	$	9.55
Expired	(8.0	)	$	10.76
Options outstanding, December 31, 2018	15,810.0		$	8.63
Granted	4,091.0		$	10.29
Exercised	(1,967.0	)	$	5.83
Forfeited	(879.0	)	$	11.07
Expired	(331.0	)	$	13.38
Options outstanding, December 31, 2019	16,724.0		$	9.15	6.4	$	30.8
Vested and unvested expected to vest, December 31, 2019	16,111.2		$	9.08	6.3	$	30.6
Exercisable at December 31, 2019	10,646.5		$	8.33	5.1	$	27.0

The aggregate intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017 was $11.8 million, $11.9 million, and $20.8 million respectively. Cash proceeds from stock options exercised during the years ended December 31, 2019, 2018, and 2017 were $11.5 million, $9.1 million, and $16.3 million, respectively. As of December 31, 2019, the total unrecognized compensation cost related to non-vested stock options granted was $32.4 million and is expected to be recognized over a weighted average period of 2.5 years.

Restricted Stock Units and Performance-Based Restricted Stock Units (collectively "RSU's")

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 year ended December 31, 2019 is as follows:



	Number of Share		Weighted Average Grant Date Fair Value		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Non-vested units as of December 31, 2017	2,575.1		$	5.85
Granted	1,811.9		$	16.11
Vested	(530.0	)	$	6.01
Forfeited	(145.0	)	$	9.65
Non-vested units as of December 31, 2018	3,712.0		$	10.59
Granted	3,526.0		$	10.92
Vested	(921.0	)	$	8.49
Forfeited	(525.0	)	$	10.52
Non-vested units as of December 31, 2019	5,792.0		$	11.18	2.4	$	56.4

For the year ended December 31, 2019, 920,782 RSUs have vested and all non-vested units are expected to vest over their normal term. As of December 31, 2019, there was $39.8 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 2.4 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:



	Years Ended December 31,
(in thousands)	2019		2018		2017
Equity compensation expense recognized in:
Research and development expense	$	17,575	$	11,740	$	10,328
Selling, general, and administrative expense	26,855		17,520		12,773
Total equity compensation expense	$	44,430	$	29,260	$	23,101