STOCKHOLDER'S EQUITY (Tables)

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Summary of Stock Option Activity

A summary of stock option activity for the year ended December 31, 2019 is as follows (in thousands, except share and per share data):

	Number of Stock Options Outstanding	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Balance at December 31, 2018	33,152,881	$	9.52	5.45	$	1,543,793
Granted	1,184,657	72.15
Exercised	(10,176,170)	8.09
Forfeited	(541,564)	39.88
Balance at December 31, 2019	23,619,804	$	12.66	4.89	$	1,191,746
Options exercisable as of December 31, 2019	22,107,017	$	9.77	4.63	$	1,168,770

Summary of RSU Activity

Activity related to RSAs and RSUs during the year ended December 31, 2019 is set forth below:

	Number of shares	Weighted Average Grant Date Fair Value
Unvested as of December 31, 2018	17,934,728	$	31.34
Granted	7,028,055	70.61
Vested	(8,023,399)	30.19
Forfeited	(3,021,923)	40.25
Unvested as of December 31, 2019	13,917,461	$	49.90

Schedule of Fair Value Assumptions for Options

The fair value of stock options granted was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2019		2018		2017
Dividend yield	—	%	—	%	—	%
Risk-free interest rate	2.37	%	2.92	%	1.88	%
Expected volatility	40.48	%	30.87	%	32.22	%
Expected term (years)	6.02		6.19		6.02

Summary of the Effect of Share-Based Compensation on the Consolidated Statements of Operations

The following table summarizes the effects of share-based compensation on the Company's consolidated statements of operations (in thousands):

	Year Ended December 31,
	2019		2018		2017
Cost of revenue	$	155	$	97	$	77
Product development	210,840		144,601		98,310
Sales and marketing	26,720		22,797		17,568
General and administrative	60,148		49,386		39,881
Total	$	297,863	$	216,881	$	155,836