STOCK-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

Allocation of recognized period costs

The following table summarizes the allocation of stock-based compensation in the consolidated statements of operations (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2020		2019		2020
Delivery costs	$	199	$	357	$	363	$	532
Sales and marketing expense	952		2,567		1,659		3,836
Research and development expense	363		1,401		566		2,004
General and administration expense	1,558		4,783		2,192		6,861
Total stock-based compensation expense	$	3,072	$	9,108	$	4,780	$	13,233

Summary of common stock option activity

Options to purchase shares of common stock generally vest over four years and expire 10 years following the date of grant. The following table summarizes changes in common stock options:

	Shares (in thousands)		Weighted-Average Exercise Price		Weighted Average Contractual Life (in years)	Aggregate Intrinsic Value(1) (in thousands)
Options outstanding — December 31, 2019	1,000		$	22.99
Granted	—		—
Exercised	(275	)	19.71			$	14,956
Forfeited	(9	)	28.71
Canceled	(1	)	28.96
Options outstanding — June 30, 2020	715		24.17		6.12	$	32,752
Exercisable — June 30, 2020	607		$	23.87	5.99	$	27,983

Summary of RSU activity

We grant restricted stock units ("RSUs") to employees and our non-employee directors. The following table summarizes changes in RSUs, inclusive of performance-based RSUs:

	Shares (in thousands)		Weighted-Average Grant Date Fair Value		Weighted-Average Remaining Contractual Term (in years)	Unamortized Compensation Costs (in thousands)
Unvested — December 31, 2019	1,741		$	18.55
Granted	1,544		38.29
Vested	(416	)	18.88
Forfeited	(242	)	22.16
Unvested — June 30, 2020	2,627		$	29.76	3.42	$	64,036