In September 2015, the Company’s board of directors adopted the 2015 Equity Incentive Plan (the “2015 Plan”), and the Company’s stockholders approved the 2015 Plan. The 2015 Plan became effective in connection with the Company’s initial public offering in October 2015. Beginning at the time the 2015 Plan became effective, no further grants may be made under the Company’s 2012 Equity Compensation Plan, as amended and restated (the “2012 Plan”). The 2015 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock unit (“RSU”) awards, performance stock awards, cash-based awards and other stock-based awards. The number of shares initially reserved for issuance under the 2015 Plan was 1,643,872 shares of common stock. The number of shares of common stock that may be issued under the 2015 Plan will automatically increase on January 1 of each year ending on January 1, 2025, in an amount equal to the lesser of (i) 4.0% of the shares of the Company’s common stock outstanding on December 31 of the preceding calendar year or (ii) an amount determined by the Company’s board of directors. The shares of common stock underlying any awards that expire, are otherwise terminated, settled in cash or repurchased by the Company under the 2015 Plan and the 2012 Plan will be added back to the shares of common stock available for issuance under the 2015 Plan. As of January 1, 2020, the number of shares of common stock that may be issued under the 2015 Plan was increased by 1,451,997 shares. As of June 30, 2020, 1,922,147 shares remained available for grant under the 2015 Plan.

In July 2017, the Company’s board of directors adopted the 2017 Inducement Plan (the “2017 Inducement Plan”). The 2017 Inducement Plan is a non-stockholder approved stock plan adopted pursuant to the “inducement exception” provided under Nasdaq listing rules. The Company had 443,000 stock options and 44,390 RSUs outstanding as of June 30, 2020 under the 2017 Inducement Plan. All shares of common stock that were eligible for issuance under the 2017 Inducement Plan after October 1, 2018, including any shares underlying any awards that expire or are otherwise terminated, reacquired to satisfy tax withholding obligations, settled in cash or repurchased by the Company in the future that would have been eligible for re-issuance under the 2017 Inducement Plan, were retired.

Upon the 2015 Plan becoming effective, no further grants can be made under the 2012 Plan. The Company granted stock options to purchase a total of 1,140,524 shares under the 2012 Plan, of which 609,628 and 745,735 were outstanding as of June 30, 2020 and December 31, 2019, respectively. Stock options granted under the 2012 Plan vested over four years and expire after ten years.

The weighted average assumptions the Company used to estimate the fair value of stock options granted during the six months ended June 30, 2020 and 2019 were as follows:

The Company recognizes compensation expense for awards over their vesting period. Compensation expense for awards includes the impact of forfeitures in the period when they occur.

The following table summarizes stock option activity for the six months ended June 30, 2020:

The weighted average grant date fair value of stock options granted during the six months ended June 30, 2020 was $0.93 per share.

Restricted Stock Units

The following table summarizes RSU activity for the six months ended June 30, 2020:


		Weighted
		Average
		Grant Date
	Number	Fair Value
	of Shares	Per Share

Outstanding as of December 31, 2019	3,592,915	$	4.62
Granted	998,385		1.26
Vested	(1,618,634)		3.09
Forfeited and cancelled	(444,265)		4.12
Outstanding as of June 30, 2020	2,528,401	$	4.36

Stock-Based Compensation

Stock-based compensation expense included in total costs and expenses on the condensed consolidated statement of operations included the following:


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Cost of revenue	$	252	$	223	$	512	$	429
Research and development		939		1,721		1,755		3,315
General and administrative		2,118		2,654		4,495		5,126
Total stock-based compensation expense	$	3,309	$	4,598	$	6,762	$	8,870

As of June 30, 2020, the Company had unrecognized stock-based compensation expense for stock options and RSUs of $8,195 and $8,604, respectively, which is expected to be recognized over weighted average periods of 1.52 years and 2.13 years, respectively.