Stock-Based Compensation and Employee Benefit Plan (Tables)

3 Months Ended

Mar. 31, 2019

Compensation Related Costs [Abstract]

Stock Option and RSU Activity

The following table summarizes the stock option activity under our stock plans during the reporting period:

	Outstanding Options
	Number of Shares		Weighted Average Exercise Price		Remaining Contractual Life (Years)	Aggregate Intrinsic Value
						(in thousands)
Balances at December 31, 2018	14,558,420		$	25.93	6.78	$	3,084
Granted	743,705		11.38
Exercised	(136,382	)	4.23
Cancelled	(111,693	)	25.44
Balances at March 31, 2019	15,054,050		25.41		6.62	4,686
Vested and expected to vest at March 31, 2019	14,690,193		25.56		6.56	4,645
Exercisable at March 31, 2019	8,555,962		28.18		4.97	3,586

RSU Activity and Related Information

A summary of our RSUs activity and related information is as follows:

	Number of Awards Outstanding		Weighted Average Grant Date Fair Value
Unvested Balance at December 31, 2018	16,784,800		$	18.74
Granted	2,525,755		12.43
Vested	(2,960,462	)	20.17
Forfeited	(101,577	)	16.44
Unvested Balance at March 31, 2019	16,248,516		17.52

Weighted-Average Valuation Assumptions

We used the following weighted-average assumptions in applying the Black-Scholes valuation model:

	Three Months Ended March 31,
	2019	2018
Risk-free interest rate	2.60% - 2.64%	2.49%
Expected term (years)	6.3 - 6.6	6.2 - 6.5
Expected dividend yield	—	—
Expected volatility	50.20%	55.10%

Employee and Non-Employee Stock-Based Compensation Expense

The following table summarizes the components of stock-based compensation expense in the consolidated statements of operations (in thousands):

	Three Months Ended March 31,
	2019		2018
Cost of revenue	$	14,372	$	1,898
Research and development	14,230		1,638
Sales and marketing	11,512		952
General and administrative	23,768		3,468
Total stock-based compensation	$	63,882	$	7,956