Stock-Based Compensation Expense (Tables)

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Stock-Based Compensation Expense

Stock-based compensation expense for restricted stock, restricted stock units, stock options and issuances of common stock pursuant to our employee stock purchase plan was classified in the accompanying consolidated statements of operations as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
	(in thousands)
Stock-based compensation expense:
Cost of revenue	$	718	$	469	$	1,291	$	843
Research and development	4,054		2,850		7,228		5,416
Sales and marketing	2,942		2,055		5,406		3,618
General and administrative	2,716		1,976		5,139		3,698
Total stock-based compensation expense	$	10,430	$	7,350	$	19,064	$	13,575

Summary of Restricted Stock and Restricted Stock Unit Activity

Restricted stock and restricted stock unit activity during the six months ended June 30, 2019 was as follows:

	Restricted Stock				Restricted Stock Units
	Shares		Weighted-Average Grant Date Fair Value		Shares		Weighted-Average Grant Date Fair Value
Unvested balance as of December 31, 2018	21,677		$	10.88	2,773,773		$	21.21
Granted	—		—		1,509,033		41.83
Vested	(21,677	)	10.88		(594,764	)	22.88
Forfeited	—		—		(174,261	)	25.31
Unvested balance as of June 30, 2019	—		$	—	3,513,781		$	29.58

Summary of Stock Option Activity

Stock option activity during the six months ended June 30, 2019 was as follows:

	Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018	3,713,179		$	10.32
Granted	—		—
Exercised	(549,612	)	11.02			$	21,286
Forfeited/cancelled	(26,013	)	12.88
Outstanding as of June 30, 2019	3,137,554		$	10.17	5.7	$	149,561
Vested and exercisable as of June 30, 2019	2,416,849		$	8.90	5.1	$	118,275