Stock-Based Compensation - Narrative (Detail)		1 Months Ended					12 Months Ended
	Dec. 03, 2013 USD ($)	Oct. 31, 2018	Sep. 30, 2018	Mar. 31, 2018 shares	Mar. 31, 2017 shares	Jun. 30, 2012 shares	Dec. 31, 2018 USD ($) purchase_period offering_period $ / shares shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	May 31, 2018 shares	Dec. 04, 2013 shares	Dec. 31, 2010 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised | $							$ 11,800,000	$ 14,300,000	$ 24,000
Stock-based compensation | $							15,492,000	$ 6,155,000	$ 7,353,000
Limit on purchases under the ESPP per calendar year | $							$ 25,000
Common stock reserved for future issuance (shares)							5,745,000	4,561,000
Shares subject to outstanding common stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation | $							$ (3,500,000)	$ (700,000)
Total unrecognized compensation costs | $							$ 29,600,000
Percentage of outstanding options that vested (percent)			90.00%
Percentage of outstanding options that were canceled (percent)		10.00%
Recognition over weighted average periods							2 years 7 months 6 days
Shares subject to outstanding restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock units granted (in shares)					154,000		146,000
Weighted-average grant date fair value per share, granted (in usd per share) | $ / shares							$ 42.76
Stock-based compensation | $							$ 0
Restricted stock units vested (in shares)							98,000	0	0
Weighted average remaining contractual term							1 year 8 months 12 days
Intrinsic value of restricted stock units, nonvested | $							$ 4,900,000
Intrinsic value of RSUs that vested | $							4,200,000
Total unrecognized compensation costs | $							$ 1,600,000
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (shares)							1,684,000	872,000
2006 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term								10 years
2006 Plan [Member] | Shares subject to outstanding common stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting term								4 years
2010 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved												280,459
Expected term							10 years
Vesting term							4 years
Restated 2010 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved						1,162,500	1,550,351	756,524
Percent of additional shares authorized provision						4.00%
Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved							118,325	102,276		637,500	337,500
Maximum amount deductible | $	$ 1,000,000.0
Employee Stock Purchase Plan [Member] | Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved							15,243	16,672
Duration of each offering period under the ESPP							12 months
Number of purchase periods permitted under the ESPP | purchase_period							2
Duration of each purchase period under the ESPP							6 months
Number of offering periods permitted under the ESPP | offering_period							2
Percentage of purchase price							85.00%
Maximum percentage of employee withholding							20.00%
Maximum number of shares per employee							2,500
Common stock reserved for future issuance (shares)							15,243	16,672
Number of shares purchased during period (shares)							32,679	35,934	35,164
Non-employee Director [Member] | Shares subject to outstanding common stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved				20,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized				15,000