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Income Taxes - Additional Information (Detail) - USD ($) |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Taxes [Line Items] |  |  |  |
Deferred tax assets |  | $ 362,700,000 | $ 463,500,000 |
Deferred tax liabilities |  | 31,800,000 | 0 |
Research and development tax credit carry forwards |  | $ 47,500,000 | $ 38,800,000 |
Corporate tax rate |  | 35.00% | 35.00% | 35.00%
Deferred tax assets, valuation allowance |  | $ 330,900,000 | $ 463,500,000 |
Percentage of uncertain tax positions likelihood of being sustained |  | 50.00% |  |
Accrual interest or penalties |  | $ 0 | 0 |
Increases related to current year tax positions |  | 3,291,000 | $ 2,211,000 | $ 2,584,000
Unrecognized tax benefits that would affect effective tax rate |  | 30,700,000 |  |
Subsequent Event |  |  |  |
Income Taxes [Line Items] |  |  |  |
Corporate tax rate | 21.00% |  |  |
Federal |  |  |  |
Income Taxes [Line Items] |  |  |  |
Operating loss carry forward, net |  | $ 978,700,000 |  |
Operating loss carry forward beginning expiration year |  | 2021 |  |
Research and development tax credit carry forwards |  | $ 48,200,000 |  |
Alternative Minimum Tax credit carry forwards |  | $ 100,000 |  |
Federal | R&D |  |  |  |
Income Taxes [Line Items] |  |  |  |
Tax credit carry forwards beginning expiration year |  | 2018 |  |
State and Local Jurisdiction |  |  |  |
Income Taxes [Line Items] |  |  |  |
Operating loss carry forward, net |  | $ 535,300,000 |  |
Research and development tax credit carry forwards |  | $ 34,600,000 |  |
State and Local Jurisdiction | California |  |  |  |
Income Taxes [Line Items] |  |  |  |
Operating loss carry forward beginning expiration year |  | 2018 |  |
State and Local Jurisdiction | Other States |  |  |  |
Income Taxes [Line Items] |  |  |  |
Operating loss carry forward beginning expiration year |  | 2027 |  |

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- Definition Amount of deferred tax liability attributable to taxable temporary differences. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(15)(b)(2)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(15)(2)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: 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(26)(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: 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(26)(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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