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Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 10, 2015 shares | Dec. 31, 2016 USD ($) Period $ / shares shares | Dec. 31, 2015 USD ($) $ / shares shares | Dec. 31, 2014 USD ($) $ / shares | Aug. 31, 2016 shares | Jun. 12, 2013 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Total intrinsic value of options exercised | $ |  | $ 1.9 | $ 1.2 | $ 3.8 |  |
Stock-based compensation, expected dividend yield |  | 0.00% |  |  |  |
Weighted average grant-date fair value of stock options granted | $ / shares |  | $ 2.55 | $ 2.35 | $ 3.28 |  |
Stock Options |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Stock-based compensation expense expected to be recognized | $ |  | $ 11.2 |  |  |  |
Stock-based compensation, weighted average recognition period |  | 2 years 4 months 24 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 | $ |  | $ 2.6 |  |  |  |
Stock-based compensation, weighted average recognition period |  | 2 years 2 months 12 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 |  |  |  |
Increase in shares of common stock authorized for issuance | 1,500,000 | 1,320,500 |  |  |  |
Aggregate number of shares of common stock reserved for future issuance |  | 1,438,211 |  |  |  |
Stock-based compensation, expected dividend yield |  | 0.00% | 0.00% | 0.00% |  |
Weighted average grant-date fair value of awards granted | $ / shares |  | $ 1.87 | $ 1.54 | $ 1.42 |  |
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% |  |  |  |
Increase in shares of common stock authorized for issuance | 5,000,000 |  |  |  |  |
Aggregate number of shares of common stock reserved for future issuance |  | 21,600,000 |  |  |  |
Employee Stock Purchase Plan, authorized shares for issuance |  |  |  |  |  | 19,500,000
Stock-based compensation, award term |  | 10 years |  |  |  |
Performance-based stock options, outstanding |  | 0 |  |  |  |
Outstanding options and other stock based awards |  | 15,787,000 | 14,119,000 |  |  |
Number of shares available for future issuance |  | 5,100,000 |  |  |  |
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] |  |  |  |  |  |
Stock-based compensation, vesting period |  | 3 years |  |  |  |
Number of Restricted Stock Units Outstanding |  | 739,000 | 0 |  |  |
Weighted average grant-date fair value of awards granted | $ / shares |  | $ 5.26 |  |  |  |
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 |  |  |  |
Cerus Corporation Inducement Plan |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Aggregate number of shares of common stock reserved for future issuance |  |  |  |  | 1,250,000 |

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- Definition Aggregate number of common shares reserved for future issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + 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://www.xbrl.org/2003/role/presentationRef -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=6415400&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&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://www.xbrl.org/2003/role/presentationRef -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=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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