Organization	9 Months Ended
Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Description of Business Prothena Corporation plc (“Prothena” or the “Company”) is a clinical-stage neuroscience company focused on the discovery and development of novel therapies with the potential to fundamentally change the course of devastating neurological disorders. Fueled by its deep scientific understanding built over decades of neuroscience research, Prothena is advancing a pipeline of therapeutic candidates for a number of indications and novel targets including Parkinson’s disease and other related synucleinopathies (prasinezumab - PRX002/RG7935, in collaboration with Roche) and ATTR amyloidosis (PRX004), as well as tau for the potential treatment of Alzheimer’s disease and other neurodegenerative disorders and TDP-43 for the potential treatment of ALS (amyotrophic lateral sclerosis) and FTD (frontotemporal dementia) (both programs in collaboration with Celgene), for which its scientific understanding of disease pathology can be leveraged. The Company was formed on September 26, 2012 under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. The Company's ordinary shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012 and currently trade on The Nasdaq Global Select Market. Liquidity and Business Risks As of September 30, 2019, the Company had an accumulated deficit of $650.3 million and cash and cash equivalents of $390.3 million. Based on the Company's business plans, management believes that the Company’s cash and cash equivalents at September 30, 2019 are sufficient to meet its obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on research and development programs significantly above current long-term plans or enters into potential licenses and or other acquisitions of complementary technologies, products or companies, the Company may need additional capital. The Company expects to continue to finance future cash needs that exceed its cash from operating activities primarily through its current cash and cash equivalents, its collaborations with Roche and Celgene, and to the extent necessary, through proceeds from public or private equity or debt financings, loans and other collaborative agreements with corporate partners or other arrangements. The Company is subject to a number of risks, including but not limited to: the uncertainty of the Company’s research and development (“R&D”) efforts resulting in future successful commercial products; obtaining regulatory approval for its product candidates; its ability to successfully commercialize its product candidates, if approved; significant competition from larger organizations; reliance on the proprietary technology of others; dependence on key personnel; uncertain patent protection; dependence on corporate partners and collaborators; and possible restrictions on reimbursement from governmental agencies and healthcare organizations, as well as other changes in the healthcare industry.

Organization

Description of Business

Prothena Corporation plc (“Prothena” or the “Company”) is a clinical-stage neuroscience company focused on the discovery and development of novel therapies with the potential to fundamentally change the course of devastating neurological disorders. Fueled by its deep scientific understanding built over decades of neuroscience research, Prothena is advancing a pipeline of therapeutic candidates for a number of indications and novel targets including Parkinson’s disease and other related synucleinopathies (prasinezumab - PRX002/RG7935, in collaboration with Roche) and ATTR amyloidosis (PRX004), as well as tau for the potential treatment of Alzheimer’s disease and other neurodegenerative disorders and TDP-43 for the potential treatment of ALS (amyotrophic lateral sclerosis) and FTD (frontotemporal dementia) (both programs in collaboration with Celgene), for which its scientific understanding of disease pathology can be leveraged.

The Company was formed on September 26, 2012 under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. The Company's ordinary shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012 and currently trade on The Nasdaq Global Select Market.

Liquidity and Business Risks

As of September 30, 2019, the Company had an accumulated deficit of $650.3 million and cash and cash equivalents of $390.3 million.

Based on the Company's business plans, management believes that the Company’s cash and cash equivalents at September 30, 2019 are sufficient to meet its obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on research and development programs significantly above current long-term plans or enters into potential licenses and or other acquisitions of complementary technologies, products or companies, the Company may need additional capital. The Company expects to continue to finance future cash needs that exceed its cash from operating activities primarily through its current cash and cash equivalents, its collaborations with Roche and Celgene, and to the extent necessary, through proceeds from public or private equity or debt financings, loans and other collaborative agreements with corporate partners or other arrangements.

The Company is subject to a number of risks, including but not limited to: the uncertainty of the Company’s research and development (“R&D”) efforts resulting in future successful commercial products; obtaining regulatory approval for its product candidates; its ability to successfully commercialize its product candidates, if approved; significant competition from larger organizations; reliance on the proprietary technology of others; dependence on key personnel; uncertain patent protection; dependence on corporate partners and collaborators; and possible restrictions on reimbursement from governmental agencies and healthcare organizations, as well as other changes in the healthcare industry.