STOCK-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [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,
	2017		2018		2017		2018
Delivery costs	$	43	$	183	$	84	$	268
Sales and marketing expense	522		2,668		866		3,611
Research and development expense	239		1,756		410		2,226
General and administration expense	438		3,738		865		5,140
Total stock-based compensation expense	$	1,242	$	8,345	$	2,225	$	11,245

Summary of common stock option activity

A summary of common stock option activity is as follows (in thousands, except per share amounts):

	Shares		Weighted-Average Exercise Price
Options outstanding — December 31, 2016	2,137		$	15.00
Granted	468		21.13
Exercised	(148	)	3.80
Forfeited	(34	)	21.41
Cancelled	(81	)	11.31
Options outstanding — June 30, 2017	2,342		$	16.97

	Shares		Weighted-Average Exercise Price
Options outstanding — December 31, 2017	2,514		$	18.42
Granted	29		24.24
Exercised	(64	)	6.40
Forfeited	(128	)	24.95
Cancelled	(119	)	18.24
Options outstanding — June 30, 2018	2,232		$	18.48

Summary of RSU activity

A summary of restricted stock unit activity is as follows (in thousands, except per share amounts):

	Shares		Weighted-Average Grant Date Fair Value
Unvested — December 31, 2017	—		$	—
Granted	1,243		20.64
Vested	—		—
Forfeited	(11	)	16.77
Unvested — June 30, 2018	1,232		$	20.68