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Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions |  | 12 Months Ended
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Jun. 05, 2019 shares | Dec. 31, 2019 USD ($) Period $ / shares shares | Dec. 31, 2018 USD ($) $ / shares shares | Dec. 31, 2017 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Total intrinsic value of options exercised | $ |  |  | $ 1.6 | $ 7.1 | $ 0.6
Stock-based compensation, expected dividend yield |  |  | 0.00% |  |
Weighted average grant-date fair value of stock options granted | $ / shares |  |  | $ 2.73 | $ 2.41 | $ 1.98
Stock Options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation expense expected to be recognized | $ |  |  | $ 6.0 |  |
Stock-based compensation, weighted average recognition period |  |  | 1 year 9 months 18 days |  |
Stock-based compensation, expected dividend yield |  |  | 0.00% | 0.00% | 0.00%
Restricted Stock Units (RSUs) |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation expense expected to be recognized | $ |  |  | $ 14.1 |  |
Stock-based compensation, weighted average recognition period |  |  | 1 year 10 months 24 days |  |
Employee Stock Purchase Plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation, option to be granted at percentage of fair value of common stock |  |  | 85.00% |  |
Employee Stock Purchase Plan, offering period |  |  | 12 months |  |
Number of purchase periods within each offering period | Period |  |  | 2 |  |
Aggregate number of shares of common stock reserved for future issuance |  |  | 600,000 |  |
Stock-based compensation, expected dividend yield |  |  | 0.00% | 0.00% | 0.00%
Weighted average grant-date fair value of awards granted | $ / shares |  |  | $ 1.84 | $ 2.29 | $ 1.18
2008 Equity Incentive Plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation, option to be granted at percentage of fair value of common stock |  |  | 100.00% |  |
Aggregate number of shares of common stock reserved for future issuance |  |  | 31,400,000 |  |
Stock-based compensation, award term |  |  | 10 years |  |
Performance-based stock options, outstanding |  |  | 35,000 |  |
Increase in shares of common stock authorized for issuance |  | 11,800,000,000 |  |  |
Outstanding options and other stock based awards |  |  | 16,830,000 | 17,560,000 |
Number of shares available for future issuance |  |  | 10,500,000 |  |
2008 Equity Incentive Plan | Stock Options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation, vesting period |  |  | 4 years |  |
2008 Equity Incentive Plan | Restricted Stock Units (RSUs) |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Number of unvested Restricted Stock Units |  |  | 4,098,000 | 2,001,000 |
Total fair value | $ |  |  | $ 5.6 | $ 2.8 | $ 1.0
Weighted average grant-date fair value of awards granted | $ / shares | [1] |  | $ 5.56 |  |
2008 Equity Incentive Plan | Performance-based Stock or Cash Awards |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Employee Stock Purchase Plan, authorized shares for issuance |  |  | 500,000 |  |
Stock option plan granted on cash award | $ |  |  | $ 1.0 |  |
2008 Equity Incentive Plan | Minimum | Restricted Stock Units (RSUs) |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation, vesting period |  |  | 3 years |  |
2008 Equity Incentive Plan | Maximum | Restricted Stock Units (RSUs) |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation, vesting period |  |  | 4 years |  |
[1] | Includes shares issuable under performance-based restricted stock unit awards.

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- Definition Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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