Stock Plans and Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Assumptions Used in Determining Fair Value of Stock Option Grants and Shares Issuable

The fair value of stock option grants and shares issuable under the ESPP is determined using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Year Ended December 31,
	2019		2018		2017
Employee Stock Options:
Fair value of common stock		—	$33.06 - $58.75		$18.05 - $26.50
Expected term (in years) (1)		—		6.00	6.00 - 6.11
Expected volatility (2)		—	45% - 50%		50% - 60%
Risk-free interest rate (3)		—	2.72% - 2.98%		1.82% - 2.47%
Dividend rate (4)		—	0%		0%
Employee Stock Purchase Plan:
Expected term (in years) (1)		0.50		0.50		0.50
Expected volatility (2)	45%		40% - 60%		60%
Risk-free interest rate (3)	1.93% - 2.52%		1.18% - 2.33%		0.45% - 1.18%
Dividend rate (4)	0%		0%		0%

⁽¹⁾ The expected term represents the period that the stock-based compensation awards are expected to be outstanding. Since the Company did not have sufficient historical information to develop reasonable expectations about future exercise behavior, the Company used the simplified method to compute expected term, which reflects the average of the time-to-vesting and the contractual life;

⁽²⁾ The expected volatility of the Company’s common stock on the date of grant is based on the weighted-average of the Company’s historical volatility as a public company and the volatilities of publicly traded peer companies that are reasonably comparable to the Company’s own operations;

⁽³⁾ The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for zero coupon U.S. Treasury notes with maturities approximately equal to the expected term of the grant; and

⁽⁴⁾ The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on the Company’s common stock.

Schedule of Stock Option Activity

The following table summarizes the Company’s stock option activity:

	Stock options outstanding			Weighted average exercise price
Outstanding at December 31, 2018		1,746,073		$	22.43
Granted		—			—
Exercised		(918,588	)		18.96
Forfeited		(104,102	)		24.44
Outstanding at December 31, 2019		723,383			26.56

Schedule of Stock Options Outstanding, Vested and Expected to Vest and Exercisable

Stock options outstanding, vested and expected to vest and exercisable are as follows:

	As of December 31, 2019
	Number of shares		Remaining contractual life (years)		Weighted- average exercise price
Outstanding		723,383		7.42	$	26.56
Vested and expected to vest		707,428		7.40		26.44
Exercisable		231,344		6.44		19.31

Schedule of Vested and Nonvested Stock Option Activity

Vested and nonvested stock option activity was as follows:

	Vested				Nonvested
	Options outstanding		Weighted average exercise price		Options outstanding		Weighted average exercise price
Outstanding at December 31, 2019		231,344	$	19.31		492,039	$	29.97

Summary of RSU, Market-based RSU and PSU Activity

The following table summarizes the Company’s RSU, market-based RSU and PSU activity for the year ended December 31, 2019:

	Number of Shares
Outstanding at December 31, 2018		904,033
Granted		809,167
Vested		(275,680	)
Forfeited		(122,729	)
Outstanding at December 31, 2019		1,314,791

Summary of Stock-Based Compensation Expense

Stock-Based Compensation Expense

The Company recorded the total stock-based compensation expense as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Cost of revenue	$	1,966	$	2,306	$	578
Sales and marketing		9,983		9,282		2,419
Research and development		7,820		7,106		1,514
General and administrative		13,720		7,131		4,788
Total	$	33,489	$	25,825	$	9,299