The potential liability for company's sale success payments.

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- Definition

Amount of market capitalization.

+ References

No definition available.

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- Definition

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ 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 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The increase (decrease) during the reporting period in current portion (due within one year or one business cycle) of obligations evidenced by formal promissory notes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The cash outflow for a borrowing supported by a written promise to pay an obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3291-108585

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- Definition

Number of shares issued in lieu of cash for services contributed to the entity. Number of shares includes, but is not limited to, shares issued for services contributed by vendors and founders.

+ References

No definition available.

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Commitments and Contingencies - Notes Payable (Details) - USD ($) $ in Thousands			1 Months Ended						12 Months Ended
	Dec. 06, 2017	Mar. 28, 2017	Jan. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Aug. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Commitments and contingencies
Accrued expenses				$ 11,049				$ 17,439	$ 11,049
Notes Payable
Notes paid in cash									600
2016 License Agreements
Commitments and contingencies
Market Capitalization				1,000,000			$ 750,000		1,000,000
Broad and Wageningen University \| Cpf1 License Agreement
Notes Payable
Promissory notes issued								$ 10,000
Interest rate (as a percentage)								4.80%
Success Payments							5,000
Broad and Wageningen University \| Cpf1 License Agreement \| Success Payment Notes
Notes Payable
Promissory notes issued							$ 5,000
The Broad Institute Inc \| 2016 License Agreements
Notes Payable
Promissory notes issued	$ 7,500	$ 5,000
The Broad Institute Inc \| Cpf1 License Agreement
Notes Payable
Common stock issued					371,166	108,104
Success Payments				$ 7,500
The Broad Institute Inc \| Cpf1 License Agreement \| Success Payment Notes
Notes Payable
Promissory notes issued									7,500
Common stock issued						271,347
The Broad Institute Inc \| Cpf1 License Agreement \| Subsequent Event \| Success Payment Notes
Notes Payable
Common stock issued			225,909
Wageningen University \| 2016 License Agreements
Notes Payable
Promissory notes issued		$ 5,000
Wageningen University \| Cpf1 License Agreement
Notes Payable
Notes paid in cash						$ 200
Wageningen University \| Cpf1 License Agreement \| Success Payment Notes
Notes Payable
Notes paid in cash						$ 400
The General Hospital (MGH) \| 2016 License Agreements
Notes Payable
Success Payments									$ 2,000
The General Hospital (MGH) \| 2016 License Agreements \| Subsequent Event
Notes Payable
Common stock issued			80,000