Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The fair value of options granted in each year using the Black-Scholes pricing model has been based on the following assumptions:

	Year Ended   December 31,
	2019	2018	2017
Volatility	39.1% - 39.5%	38.6% - 47.8%	41.7% - 44.2%
Risk-free interest rate	1.6% - 2.5%	2.6% - 2.9%	1.9% - 2.2%
Expected term (in years)	5.5 - 6.2	5.5 - 6.3	5.5 - 6.3
Dividend rate	—%	—%	—%

Schedule of Share-based Compensation, Stock Options, Activity

The following table summarizes the activity for the Company’s options (in thousands, except share and per share amounts):

	Shares		Weighted-Average Exercise Price		Weighted-Average Remaining Contract Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2016	9,339,567		$	7.89	6.64	$	43,613
Granted	5,887,183		11.04
Exercised	(5,760,263	)	5.87
Forfeited/Canceled	(1,518,548	)	11.36
Outstanding at December 31, 2017	7,947,939		11.02		7.93	74,996
Granted	797,201		29.87
Exercised	(1,588,779	)	11.49
Forfeited/Canceled	(265,367	)	15.68
Outstanding at December 31, 2018	6,890,994		12.91		7.94	239,177
Granted	462,563		64.29
Exercised	(840,835	)	11.64
Forfeited/Canceled	(217,803	)	30.11
Outstanding at December 31, 2019	6,294,919		16.26		7.24	185,900
Total exercisable at December 31, 2019	3,835,279		12.30		6.88	123,671

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value

The following table summarizes the weighted-average grant date fair value of options granted, intrinsic value of options exercised and fair value of awards vested in periods indicated (in thousands, except per share amounts):

	Year Ended December 31,
	2019		2018		2017
Weighted average grant date fair value of options granted	$	26.75	$	13.33	$	4.85
Intrinsic value of options exercised	42,758		34,268		52,693
Fair value of awards vested	41,997		32,717		19,826

Summary of the Activity of Unvested RSUs

The following table summarizes the activity for the Company’s unvested RSUs:

	Shares		Weighted-Average Fair Value
Unvested at December 31, 2016	3,135,181		$	10.70
Granted	2,360,315		12.17
Vested	(1,072,321	)	10.44
Forfeited/Canceled	(1,348,928	)	10.56
Unvested at December 31, 2017	3,074,247		11.98
Granted	2,448,169		28.22
Vested	(1,496,906	)	13.80
Forfeited/Canceled	(545,142	)	18.47
Unvested at December 31, 2018	3,480,368		22.87
Granted	1,464,785		61.92
Vested	(1,392,295	)	22.67
Forfeited/Canceled	(592,445	)	31.25
Unvested at December 31, 2019	2,960,413		40.61

Schedule of Share-based Compensation, Allocation of Recognized Period Costs

Total stock-based compensation expense included in the Consolidated Statements of Operations is as follows (in thousands):

	Year Ended   December 31,
	2019		2018		2017
Cost of revenue	$	5,787	$	3,357	$	1,739
Marketing	3,774		2,507		1,933
Product development	21,085		21,234		8,274
General and administrative	13,749		11,133		14,613
Total stock-based compensation expense	$	44,395	$	38,231	$	26,559