STOCKHOLDERS' EQUITY (Tables)

12 Months Ended

Dec. 31, 2017

Stockholders' Equity Note [Abstract]

Schedule of Stock by Class

The following table presents the number of shares authorized and issued and outstanding as of the dates indicated:

	December 31, 2017		December 31, 2016
	Shares Authorized	Shares Issued and Outstanding	Shares Authorized	Shares Issued and Outstanding
Stockholders’ equity:
Common stock, $0.000001 par value	200,000,000	83,724,916	200,000,000	79,429,833
Undesignated Preferred Stock	10,000,000	—	10,000,000	—

Schedule of Shares of Class A and Class B Common Stock Reserved for Future Issuance

As of December 31, 2017, the Company had reserved shares of common stock for future issuances in connection with the following:

	Number of Shares
Options outstanding	7,078,932
Restricted stock units and awards outstanding	7,249,205
Available for future stock option and restricted stock units and awards grants	4,845,772
Available for future ESPP offerings	2,518,929
Total reserved for future issuance	21,692,838

Schedule of Stock Option Activity

A summary of stock option activity for the year ended December 31, 2017 is as follows:

	Options Outstanding
	Number of Shares		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding-December 31, 2016	8,018,941		$	21.71	6.10 years	$	147,673
Granted	920,850		34.60
Exercised	(1,519,771	)	19.74
Canceled	(341,088	)	44.78
Outstanding-December 31, 2017	7,078,932		$	22.70	5.56 years	$	145,613
Options vested and exercisable as of December 31, 2017	5,774,043		$	20.55	4.87 years	$	131,625

Summary of RSUs and RSAs Activity

A summary of RSU activity for the year ended December 31, 2017 is as follows:

	Restricted Stock Units
	Number of Shares		Weighted- Average Grant Date Fair Value
Unvested December 31, 2016	7,090,465		$	32.43
Granted	4,647,404		37.22
Released (1)	(2,761,821	)	34.06
Canceled	(1,726,843	)	33.75
Unvested December 31, 2017	7,249,205		$	34.57

(1) Included in this balance is 58,983 shares vested but not issued due to net share settlement for payment of employee taxes

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

The Company uses the straight-line method for expense attribution. For the years ended December 31, 2017, 2016 and 2015, the weighted-average assumptions are as follows:

	Year Ended December 31,
	2017		2016		2015
Dividend yield	—		—		—
Annual risk-free rate	2.14	%	1.53	%	1.78	%
Expected volatility	44.00	%	44.00	%	49.27	%
Expected term (years)	5.90		5.84		6.11

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

The following table summarizes the effects of stock-based compensation expense related to stock-based awards in the consolidated statements of operations during the periods presented (in thousands):

	Year Ended December 31,
	2017			2016			2015
Cost of revenue	$	4,010		$	2,446		$	1,117
Sales and marketing	28,100			27,098			21,962
Product development	47,280			36,323			23,431
General and administrative	21,025			20,394			14,332
Total stock-based compensation in income (loss) before incomes taxes	100,415			86,261			60,842
Benefit from income taxes	(1,407		)	(643		)	(402		)
Total stock-based compensation in income (loss)	$	99,008		$	85,618		$	60,440