Stock-based Awards (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of stock option activity

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

	Number of Options		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life	Aggregate Intrinsic Value (1)
					(in years)	(in millions)
Outstanding at December 31, 2016	24,541,512		$	8.29	5.5
Granted	4,846,453		18.38
Exercised	(11,650,950	)	6.31
Canceled/forfeited	(1,022,799	)	10.49
Outstanding at December 31, 2017	16,714,216		$	12.46	7.7	$	21.7
Vested and expected to vest at December 31, 2017	16,714,216		$	12.46	7.7	$	21.7
Exercisable at December 31, 2017	8,005,880		$	10.73	6.5	$	13.5

(1) The aggregate intrinsic value represents the excess of the closing price of the Company’s common stock of $11.20 on December 31, 2017 over the exercise price of in-the-money stock option awards.

Schedule of activity in connection with the restricted stock units

Activity in connection with restricted stock units (“RSUs”) is as follows for the year ended December 31, 2017:

	Number of Shares		Weighted-Average Grant Date Fair Value
Non-vested — December 31, 2016	4,339,320		$	7.85
Granted	2,086,878		18.26
Vested	(1,681,447	)	9.60
Canceled/forfeited	(460,313	)	10.10
Non-vested — December 31, 2017	4,284,438		$	11.99

Schedule of fair value of stock option awards

The fair value of each stock option award was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:

	Year Ended December 31,
	2017		2016		2015
Risk-free interest rate	1.89	%	1.32	%	1.66	%
Expected term (years)	6.25		5.96		6.03
Expected volatility	47	%	49	%	49	%
Dividend yield	—		—		—

Schedule of stock-based compensation cost relating to stock options, restricted stock awards and RSUs

The Company recorded stock-based compensation cost relating to stock options, restricted stock awards, and RSUs in the following categories on the accompanying consolidated statements of comprehensive loss (in thousands):

	Year Ended December 31,
	2017		2016		2015
Cost of revenue	$	1,105	$	960	$	792
Sales and marketing	10,353		5,837		4,493
Technology and development	8,060		4,398		4,294
General and administrative	12,723		13,544		32,984
Total stock-based compensation expense	32,241		24,739		42,563
Amount capitalized to internal-use software	1,407		1,012		1,325
Total stock-based compensation cost	$	33,648	$	25,751	$	43,888