Stock-Based Compensation - Summary of Stock Options Outstanding by Exercise Price Range (Detail)	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, number of options (in shares) | shares	12,707,037
Options outstanding, weighted average exercise price (in dollars per share)	$ 3.56
Options outstanding, weighted average remaining contractual term (in years)	7 years 5 months 12 days
Options vested and exercisable, number of options (in shares) | shares	7,553,273
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 4.34
Options vested and exercisable, weighted average remaining contractual term (in years)	6 years 3 months 12 days
$0.12 to 2.39
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	$ 0.12
Range of exercise prices, upper limit (in dollars per share)	$ 2.39
Options outstanding, number of options (in shares) | shares	3,107,393
Options outstanding, weighted average exercise price (in dollars per share)	$ 1.72
Options outstanding, weighted average remaining contractual term (in years)	7 years 5 months 12 days
Options vested and exercisable, number of options (in shares) | shares	1,536,600
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 1.71
Options vested and exercisable, weighted average remaining contractual term (in years)	5 years 6 months 12 days
$2.46 to 2.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	$ 2.46
Range of exercise prices, upper limit (in dollars per share)	$ 2.60
Options outstanding, number of options (in shares) | shares	4,087,859
Options outstanding, weighted average exercise price (in dollars per share)	$ 2.52
Options outstanding, weighted average remaining contractual term (in years)	6 years 9 months 12 days
Options vested and exercisable, number of options (in shares) | shares	2,823,284
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 2.54
Options vested and exercisable, weighted average remaining contractual term (in years)	6 years 2 months 12 days
$2.62 to 2.72
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	$ 2.62
Range of exercise prices, upper limit (in dollars per share)	$ 2.72
Options outstanding, number of options (in shares) | shares	3,215,695
Options outstanding, weighted average exercise price (in dollars per share)	$ 2.66
Options outstanding, weighted average remaining contractual term (in years)	9 years 1 month 12 days
Options vested and exercisable, number of options (in shares) | shares	1,115,374
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 2.68
Options vested and exercisable, weighted average remaining contractual term (in years)	8 years 7 months 12 days
$2.76 to 8.77
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	$ 2.76
Range of exercise prices, upper limit (in dollars per share)	$ 8.77
Options outstanding, number of options (in shares) | shares	1,008,356
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.50
Options outstanding, weighted average remaining contractual term (in years)	6 years 5 months 12 days
Options vested and exercisable, number of options (in shares) | shares	823,328
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 5.94
Options vested and exercisable, weighted average remaining contractual term (in years)	6 years 12 days
$8.92 to 27.03
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	$ 8.92
Range of exercise prices, upper limit (in dollars per share)	$ 27.03
Options outstanding, number of options (in shares) | shares	1,287,734
Options outstanding, weighted average exercise price (in dollars per share)	$ 12.07
Options outstanding, weighted average remaining contractual term (in years)	5 years 7 months 12 days
Options vested and exercisable, number of options (in shares) | shares	1,254,687
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 12.06
Options vested and exercisable, weighted average remaining contractual term (in years)	5 years 7 months 12 days