Stockholders' Equity - Summary of Stock Options Outstanding (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	8,287,456
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	6 years 8 months 8 days
Options Exercisable Number of Shares of common stock subject to options | shares	3,881,078
Options Exercisable Weighted Average Exercise Price	$ 8.99
$2.55 – $3.45 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	2.55
Upper Range of Exercise Price	$ 3.45
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	612,318
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	7 years 11 months 1 day
Options Exercisable Number of Shares of common stock subject to options | shares	214,920
Options Exercisable Weighted Average Exercise Price	$ 3.13
$3.50 – $3.50 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	3.50
Upper Range of Exercise Price	$ 3.50
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	1,527,625
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	9 years 25 days
$3.55 – $5.41 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	$ 3.55
Upper Range of Exercise Price	$ 5.41
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	1,212,567
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	5 years 2 months 26 days
Options Exercisable Number of Shares of common stock subject to options | shares	672,930
Options Exercisable Weighted Average Exercise Price	$ 5.34
$5.42 – $7.07 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	5.42
Upper Range of Exercise Price	$ 7.07
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	1,501,051
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	5 years 6 months 10 days
Options Exercisable Number of Shares of common stock subject to options | shares	967,506
Options Exercisable Weighted Average Exercise Price	$ 6.11
$7.20 – $9.41 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	7.20
Upper Range of Exercise Price	$ 9.41
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	1,199,546
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	7 years 2 months 1 day
Options Exercisable Number of Shares of common stock subject to options | shares	551,162
Options Exercisable Weighted Average Exercise Price	$ 9.06
$9.45 – $13.35 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	9.45
Upper Range of Exercise Price	$ 13.35
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	885,599
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	5 years 6 months 7 days
Options Exercisable Number of Shares of common stock subject to options | shares	659,946
Options Exercisable Weighted Average Exercise Price	$ 11.92
$13.54 – $15.00 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	13.54
Upper Range of Exercise Price	$ 15
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	1,148,250
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	6 years 3 months 3 days
Options Exercisable Number of Shares of common stock subject to options | shares	668,752
Options Exercisable Weighted Average Exercise Price	$ 14.07
$15.11 – $18.26 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	15.11
Upper Range of Exercise Price	$ 18.26
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	178,000
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	7 years 3 months 21 days
Options Exercisable Number of Shares of common stock subject to options | shares	124,561
Options Exercisable Weighted Average Exercise Price	$ 16.41
$19.51 – $19.51 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	19.51
Upper Range of Exercise Price	$ 19.51
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	10,000
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	6 years 1 month 20 days
Options Exercisable Number of Shares of common stock subject to options | shares	9,583
Options Exercisable Weighted Average Exercise Price	$ 19.51
$19.80 – $19.80 [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Lower Range of Exercise Price	19.80
Upper Range of Exercise Price	$ 19.80
Options Outstanding and Exercisable Number of Shares of common stock subject to options | shares	12,500
Options Outstanding and Exercisable Weighted Average Remaining Contractual Life (In years)	6 years 2 months 23 days
Options Exercisable Number of Shares of common stock subject to options | shares	11,718
Options Exercisable Weighted Average Exercise Price	$ 19.80