Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock-based compensation expense

Stock-based compensation expense included in the consolidated statements of operations was as follows:

	Three Months Ended March 31,
(in thousands)	2020		2019
Cost of revenue	$	747	$	652
Sales and marketing	4,496		3,366
Research and development	2,948		2,030
General and administrative	4,844		3,271
Total stock-based compensation expense	$	13,035	$	9,319

Stock option activity

A summary of our stock option activity is presented below:

(in thousands, except for per share data and years)	Number of Shares	Weighted Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2019	12,939	$	8.38	7.1	$	201,608
Granted	—	—
Exercised	(635)	6.27			12,383
Forfeited/canceled	(190)	10.78
Outstanding at March 31, 2020	12,114	8.45		7.0	162,596
Exercisable at March 31, 2020	6,783	6.12		6.5	106,847

Summary of restricted stock and restricted stock units

A summary of our restricted stock and restricted stock units activity is presented below:

	Restricted Stock				Restricted Stock Units
(in thousands, except for per share data)	Number of Shares		Weighted Average Grant Date Fair Value		Number of Shares		Weighted Average Grant Date Fair Value
Unvested balance at December 31, 2019	495		$	4.25	2,894		$	26.34
Granted	—		—		3,082		28.00
Vested	(99	)	4.25		(403	)	29.14
Forfeited	—		—		(123	)	26.16
Unvested balance at March 31, 2020	396		4.25		5,450		27.07

ESPP valuation assumptions

The fair value of the 2018 ESPP purchase rights was estimated on the offering or modification dates using a Black-Scholes option-pricing model and the following assumptions:

	Three Months Ended March 31,
	2020	2019
Expected term (in years)	0.5 — 2.0	0.5 — 2.0
Expected volatility	41.6% — 47.9%	35.4% — 44.6%
Risk-free interest rate	0.8% — 0.9%	2.5% — 2.6%
Expected dividend yield	—	—