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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Significant Accounting Policies [Line Items] |  |  |
Decrease in cash flows from financing activities by adoption of accounting pronouncements |  | $ (35,400) | $ (948)
Reduction to research and development expenses |  | 100 | 100
Accounts receivable |  | 24 | $ 31
ISU Abxis |  |  |
Significant Accounting Policies [Line Items] |  |  |
Accounts receivable |  | $ 20 |
Software |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives |  | 3 years |
Computer equipment |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives |  | 3 years |
Laboratory and office equipment | Minimum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives |  | 3 years |
Laboratory and office equipment | Maximum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives |  | 7 years |
Furniture | Minimum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives |  | 3 years |
Furniture | Maximum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives |  | 7 years |
Leasehold improvements | Minimum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives |  | 3 years |
Leasehold improvements | Maximum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives |  | 7 years |
Scenario Forecast | ASU 2016-18 |  |  |
Significant Accounting Policies [Line Items] |  |  |
Decrease in cash flows from financing activities by adoption of accounting pronouncements | $ 14,300 |  |

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- Definition Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business. + 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(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: 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(5)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition Amount of cash inflow (outflow) of financing activities, excluding discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 26 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3574-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3521-108585 + Details
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