Stock-Based Compensation - Narrative (Detail)		1 Months Ended				12 Months Ended
	Jan. 01, 2020 shares	Oct. 31, 2018	Sep. 30, 2018	Mar. 31, 2017 shares	Oct. 31, 2015	Dec. 31, 2019 USD ($) purchase_period offering_period shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	May 21, 2019 shares	May 20, 2019 shares	May 31, 2018 shares	Dec. 31, 2013 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (shares)						9,646,000	5,745,000
Intrinsic value of options exercised | $						$ 22,400,000	$ 11,800,000	$ 14,300,000
Stock-based compensation (reversal) | $						21,247,000	$ 15,492,000	6,155,000
Shares subject to outstanding common stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation costs | $						$ 58,200,000
Recognition over weighted average periods						2 years 8 months 12 days
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (shares)						4,926,000	1,684,000
Shares subject to outstanding restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting term						5 years
Restricted stock units vested (in shares)						37,000
Intrinsic value of RSUs that vested | $						$ 1,900,000	$ 4,200,000
Number of restricted stock units granted (in shares)				130,000		235,000
Stock-based compensation (reversal) | $						$ 0
Weighted average remaining contractual term						1 year 6 months
Intrinsic value of restricted stock units, nonvested | $						$ 16,100,000
Total unrecognized compensation costs | $						$ 1,400,000
Performance-based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting term					3 years
Stock-based compensation (reversal) | $							$ 3,500,000	$ (700,000)
Percentage of outstanding options that vested (percent)			90.00%
Percentage of awards that were cancelled (percent)		10.00%
2006 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved						20,218
2010 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved										7,500,000
Expected term						10 years
Vesting term						4 years
Restated 2010 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved						4,907,684			11,500,000
Percent of additional shares authorized provision						4.00%
Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved											637,500	337,500
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limit on purchases under the ESPP per calendar year | $						$ 25,000
Employee Stock Purchase Plan | Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term						10 years
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)						18,347
Increase in shares available for purchase (shares)	31,250
Number of shares purchased during period (shares)						28,146	32,679	35,934