Stock-Based Compensation

6 Months Ended

Jun. 30, 2021

Share-based Payment Arrangement [Abstract]

Stock-based compensation expense is included in the following line items in the condensed consolidated statements of operations (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Sales and marketing	$	1,235	$	772	$	2,043	$	1,529
General and administrative	3,163		2,097		5,243		3,879
Research and development	5,658		4,226		10,658		8,045
Total stock-based compensation expense	$	10,056	$	7,095	$	17,944	$	13,453

The following table summarizes the components of non-cash stock-based compensation expense (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Stock options and assumed options	$	1,159	$	1,015	$	1,776	$	1,816
Restricted stock units	8,849		6,048		16,073		11,558
Employee stock purchase plan	48		32		95		79
Total stock-based compensation expense	$	10,056	$	7,095	$	17,944	$	13,453
Tax windfall benefit from stock-based awards	$	3,120	$	1,610	$	5,680	$	2,188

We granted an aggregate of 133,700 stock options pursuant to our 2015 Equity Incentive Plan, or the 2015 Plan, during each of the three and six months ended June 30, 2021, as compared to an aggregate of 136,650 and 141,650 stock options for the same periods in the prior year. There were 63,083 and 136,258 stock options exercised during the three and six months ended June 30, 2021, respectively, as compared to 194,443 and 258,191 stock options for the same periods in the prior year. We granted an aggregate of 428,194 and 555,410 restricted stock units during the three and six months ended June 30, 2021, respectively, as compared to an aggregate of 218,344 and 319,072 restricted stock units for the same periods in the prior year. The restricted stock units granted during the three and six months ended June 30, 2021 included 120,314 of performance-based stock awards. There were no performance-based restricted stock units granted during the three and six months ended June 30, 2020. There were 173,553 and 262,923 restricted stock units that vested during the three and six months ended June 30, 2021, respectively, as compared to 64,075 and 87,123 restricted stock units vested during the same periods in the prior year. There were no performance-based restricted stock units that vested during the three months ended June 30, 2021 and there were 20,000 performance-based restricted stock units that vested during the six months ended June 30, 2021. There were no performance-based restricted stock units that vested during the three and six months ended June 30, 2020.