STOCK-BASED COMPENSATION (Tables)

3 Months Ended

Mar. 31, 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 March 31,
	2017		2018
Delivery costs	$	41	$	85
Sales and marketing expense	344		943
Research and development expense	171		470
General and administration expense	427		1,402
Total stock-based compensation expense	$	983	$	2,900

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	124		11.81
Exercised	(76	)	3.57
Forfeited	(9	)	20.59
Cancelled	(6	)	14.21
Options outstanding — March 31, 2017	2,170		$	15.20

	Shares		Weighted-Average Exercise Price
Options outstanding — December 31, 2017	2,514		$	18.42
Granted	29		24.24
Exercised	(26	)	4.22
Forfeited	(103	)	25.65
Cancelled	(35	)	15.88
Options outstanding — March 31, 2018	2,379		$	18.37

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	1,210		20.80
Vested	—		—
Forfeited	(2	)	16.80
Unvested — March 31, 2018	1,208		$	20.81