Related Parties	6 Months Ended
Jun. 30, 2013
Related Party Transactions [Abstract]
Related Parties	7. Related Parties Prior to December 20, 2012, the Prothena Business operated as part of Elan and not as a separate stand-alone entity. Effective December 20, 2012, the Prothena Business separated from Elan. In connection with the plan of separation, Elan acquired an 18% interest in the Company (as calculated immediately following the acquisition). As described elsewhere in these consolidated financial statements, the results of operations of the Prothena business for the time period prior to the separation include transactions with Elan. All of the revenue recognized by the Company for the three and six months ended June 30, 2013 consisted of fees arising from R&D services provided to Elan. Additionally, the results of operations for this time period include certain costs allocated from Elan to the Company for centralized support services. The Company has entered into certain agreements with Elan, including the Transitional Services Agreement and the R&D Services Agreement. Transitional Services Agreement In December 2012, the Company entered into a Transitional Services Agreement (“TSA”) with Elan under which Elan will provide to the Company, and the Company will provide to Elan, specified services to help ensure an orderly transition following the separation and distribution. The services provided by Elan under the Transitional Services Agreement will include chemistry, manufacturing and controls/quality assurance, information services, IT services, facilities services, company secretarial services, finance services, legal services, compliance services and human relations services. The services provided by the Company will include finance services and product support services and assisting in reviewing proposed Elan publications related to work done at Elan prior to separation. The Company expects that the TSA will remain in effect until the expiration of the last time period for the performance of services thereunder, which in no event shall be later than December 31, 2013. Both the Company and Elan will be permitted to terminate the TSA (to the extent it relates to any particular transitional service) if the other party breaches any of its significant obligations under the agreement and does not cure such breach within 20 business days of receiving written notice from the other party. In addition, either party may terminate the TSA if a receiver, examiner or administrator is appointed with respect to any of the other party’s assets, the other company is struck off the Register of Companies in its jurisdiction of organization or at the option of such party with respect to a particular transition service if such party is the service recipient. The payment terms of the agreement generally provide that the Company will pay Elan for the time spent by each Elan employee providing the services, which will be calculated by the portion of the employee’s time dedicated to the provision of the services, plus 40%. The time for each employee will be calculated using one of two specified rates per annum depending on the employee’s wage band. Similarly, Elan will pay the Company for the time spent by each of the Company’s employee providing services to Elan, which will be an agreed percentage of the employee’s time, based on the cost of providing those services plus 40% and including, as applicable, any fees for any services from Elan or the Company provided by third party providers and invoiced to the recipient at cost. The services from the Company will also be calculated using one of two specified rates per annum depending on the employee’s wage band. TSA expenses recognized during the three and six months ended June 30, 2013 was $Nil and $0.5 million, respectively, of which $0.1 million was included in R&D expense and $0.4 million was included in general and administrative expense. R&D Services Agreement In December 2012, The Company entered into a Research and Development Services Agreement (“RDSA”) with Elan pursuant to which the Company will provide certain R&D services to Elan. The RDSA will, among other things, set out the scope of the services, the consideration to be paid for the services and the general principles around ownership of intellectual property as it relates to the services. The RDSA is expected to be in effect for a period of not less than two years. Either party is entitled to terminate the RDSA at any time by notice in writing to the other party if there has been a material breach by the other party or if the other party becomes insolvent or if the other party is in breach of any of its confidentiality obligations under the agreement. The amounts earned under this RDSA are recognized as related party revenues on the Condensed Consolidated Statement of Operations. The services provided for under the RDSA include support for the ELND005 program (which include the provision of expert advice and opinion in the areas of nonclinical safety/toxicology and pharmacology, regulatory support for nonclinical sections of pertinent documents, conducting and interpreting externally conducted nonclinical studies, and support in respect of the identification and maintenance of nonclinical expert advisors as required). These services will be substantially similar to research services performed by the Company for Elan prior to the separation and distribution. There is also a fixed monthly charge of $7,500 to account for lab space and capital equipment used by Elan. The payment terms of the RDSA provide that Elan will pay the Company: (i) a fixed charge of $500,000 per year based on a charge for two of the Company’s employees providing the services at a rate of $250,000 each per annum, (ii) if the $500,000 fixed charge has been paid in any year, a variable charge of $250,000 per year for any additional employee that provides services for such year (calculated pro rata based on the number of days the employee provides services in such year), (iii) research costs including direct overheads and (iv) a mark-up of 10% applied to the fixed charge, variable charge (if any) and research costs such that the total payment reflects a cost-plus standard.

7. Related Parties

Prior to December 20, 2012, the Prothena Business operated as part of Elan and not as a separate stand-alone entity. Effective December 20, 2012, the Prothena Business separated from Elan. In connection with the plan of separation, Elan acquired an 18% interest in the Company (as calculated immediately following the acquisition).

As described elsewhere in these consolidated financial statements, the results of operations of the Prothena business for the time period prior to the separation include transactions with Elan. All of the revenue recognized by the Company for the three and six months ended June 30, 2013 consisted of fees arising from R&D services provided to Elan. Additionally, the results of operations for this time period include certain costs allocated from Elan to the Company for centralized support services.

The Company has entered into certain agreements with Elan, including the Transitional Services Agreement and the R&D Services Agreement.

Transitional Services Agreement

In December 2012, the Company entered into a Transitional Services Agreement (“TSA”) with Elan under which Elan will provide to the Company, and the Company will provide to Elan, specified services to help ensure an orderly transition following the separation and distribution. The services provided by Elan under the Transitional Services Agreement will include chemistry, manufacturing and controls/quality assurance, information services, IT services, facilities services, company secretarial services, finance services, legal services, compliance services and human relations services. The services provided by the Company will include finance services and product support services and assisting in reviewing proposed Elan publications related to work done at Elan prior to separation.

The Company expects that the TSA will remain in effect until the expiration of the last time period for the performance of services thereunder, which in no event shall be later than December 31, 2013.

Both the Company and Elan will be permitted to terminate the TSA (to the extent it relates to any particular transitional service) if the other party breaches any of its significant obligations under the agreement and does not cure such breach within 20 business days of receiving written notice from the other party. In addition, either party may terminate the TSA if a receiver, examiner or administrator is appointed with respect to any of the other party’s assets, the other company is struck off the Register of Companies in its jurisdiction of organization or at the option of such party with respect to a particular transition service if such party is the service recipient.

The payment terms of the agreement generally provide that the Company will pay Elan for the time spent by each Elan employee providing the services, which will be calculated by the portion of the employee’s time dedicated to the provision of the services, plus 40%. The time for each employee will be calculated using one of two specified rates per annum depending on the employee’s wage band. Similarly, Elan will pay the Company for the time spent by each of the Company’s employee providing services to Elan, which will be an agreed percentage of the employee’s time, based on the cost of providing those services plus 40% and including, as applicable, any fees for any services from Elan or the Company provided by third party providers and invoiced to the recipient at cost. The services from the Company will also be calculated using one of two specified rates per annum depending on the employee’s wage band.

TSA expenses recognized during the three and six months ended June 30, 2013 was $Nil and $0.5 million, respectively, of which $0.1 million was included in R&D expense and $0.4 million was included in general and administrative expense.

R&D Services Agreement

In December 2012, The Company entered into a Research and Development Services Agreement (“RDSA”) with Elan pursuant to which the Company will provide certain R&D services to Elan. The RDSA will, among other things, set out the scope of the services, the consideration to be paid for the services and the general principles around ownership of intellectual property as it relates to the services. The RDSA is expected to be in effect for a period of not less than two years. Either party is entitled to terminate the RDSA at any time by notice in writing to the other party if there has been a material breach by the other party or if the other party becomes insolvent or if the other party is in breach of any of its confidentiality obligations under the agreement. The amounts earned under this RDSA are recognized as related party revenues on the Condensed Consolidated Statement of Operations.

The services provided for under the RDSA include support for the ELND005 program (which include the provision of expert advice and opinion in the areas of nonclinical safety/toxicology and pharmacology, regulatory support for nonclinical sections of pertinent documents, conducting and interpreting externally conducted nonclinical studies, and support in respect of the identification and maintenance of nonclinical expert advisors as required). These services will be substantially similar to research services performed by the Company for Elan prior to the separation and distribution. There is also a fixed monthly charge of $7,500 to account for lab space and capital equipment used by Elan.

The payment terms of the RDSA provide that Elan will pay the Company: (i) a fixed charge of $500,000 per year based on a charge for two of the Company’s employees providing the services at a rate of $250,000 each per annum, (ii) if the $500,000 fixed charge has been paid in any year, a variable charge of $250,000 per year for any additional employee that provides services for such year (calculated pro rata based on the number of days the employee provides services in such year), (iii) research costs including direct overheads and (iv) a mark-up of 10% applied to the fixed charge, variable charge (if any) and research costs such that the total payment reflects a cost-plus standard.