Subsequent Events	12 Months Ended
Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Operating Leases In February 2019, we entered into the eighth lease amendment ("Eighth Amendment") with MetLife to extend the lease term for the Penobscot Space, the Building 2 Space and the 501 Chesapeake Space for another 88 months. The various terms for these properties have expiration dates that range from May 2027 to May 2029. The terms include an optional renewal period of 5 years after the expiration date based on fair market rates for comparable transactions in the geographic area described in the Eighth Amendment. The Eighth Amendment requires us to install certain improvements to the buildings. On completion of the improvements to the building, the landlord will reimburse us up to a contractually specified amount and the landlord will become the owner of the improvements. Pursuant to the terms of the Eighth Amendment, we exercised our right to deliver a letter of credit in lieu of a security deposit. The letters of credit are collateralized by deposit balances held by the bank in the amount of $1.1 million in 2019. These deposits will be recorded as restricted cash on the consolidated balance sheets. Total future minimum lease payments under the Eighth Amendment is $32.9 million. FDA Approval and Nestlé Health Science Exercises Option for Exclusive Global License to CDX-6114 In January 2019, we received notice from the U.S. Food and Drug Administration (the “FDA”) that it had completed its review of our investigational new drug application (“IND”) for CDX-6114 and concluded that we may proceed with the proposed Phase 1b multiple ascending dose study in healthy volunteers in the United States. In February 2019, Nestlé Health Science exercised its option to obtain an exclusive, worldwide, royalty-bearing, sublicensable license to develop and commercialize certain products based on the our novel, orally delivered enzyme IND for the management of phenylketonuria. Nestlé Health Science was granted this option under the Development, Option and Licensing Agreement with Codexis announced in October 2017. The exercise of the option triggered a $3 million milestone payment from Nestlé Health Science to Codexis. Upon exercising its option, Nestlé Health Science has assumed all responsibilities for future clinical development and commercialization of CDX-6114, with the exception of the completion of an extension study, CDX - 6114-004, which is expected to be completed in the second quarter of 2019.

Subsequent Events

Operating Leases

In February 2019, we entered into the eighth lease amendment ("Eighth Amendment") with MetLife to extend the lease term for the Penobscot Space, the Building 2 Space and the 501 Chesapeake Space for another 88 months. The various terms for these properties have expiration dates that range from May 2027 to May 2029. The terms include an optional renewal period of 5 years after the expiration date based on fair market rates for comparable transactions in the geographic area described in the Eighth Amendment. The Eighth Amendment requires us to install certain improvements to the buildings. On completion of the improvements to the building, the landlord will reimburse us up to a contractually specified amount and the landlord will become the owner of the improvements. Pursuant to the terms of the Eighth Amendment, we exercised our right to deliver a letter of credit in lieu of a security deposit. The letters of credit are collateralized by deposit balances held by the bank in the amount of $1.1 million in 2019. These deposits will be recorded as restricted cash on the consolidated balance sheets. Total future minimum lease payments under the Eighth Amendment is $32.9 million.

FDA Approval and Nestlé Health Science Exercises Option for Exclusive Global License to CDX-6114

In January 2019, we received notice from the U.S. Food and Drug Administration (the “FDA”) that it had completed its review of our investigational new drug application (“IND”) for CDX-6114 and concluded that we may proceed with the proposed Phase 1b multiple ascending dose study in healthy volunteers in the United States.

In February 2019, Nestlé Health Science exercised its option to obtain an exclusive, worldwide, royalty-bearing, sublicensable license to develop and commercialize certain products based on the our novel, orally delivered enzyme IND for the management of phenylketonuria. Nestlé Health Science was granted this option under the Development, Option and Licensing Agreement with Codexis announced in October 2017. The exercise of the option triggered a $3 million milestone payment from Nestlé Health Science to Codexis. Upon exercising its option, Nestlé Health Science has assumed all responsibilities for future clinical development and commercialization of CDX-6114, with the exception of the completion of an extension study, CDX - 6114-004, which is expected to be completed in the second quarter of 2019.