Prothena (PRTA) 10-Q 4 Nov 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014	Oct. 24, 2014
Document Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Trading Symbol	'PRTA	'
Entity Registrant Name	'Prothena Corp plc	'
Entity Central Index Key	'0001559053	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Accelerated Filer	'
Entity Ordinary Shares Outstanding	'	27,384,124

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$306,153	$176,677
Receivable from Roche	967	0
Receivable from related party	92	58
Deferred tax assets	89	81
Prepaid expenses and other current assets	1,518	1,406
Total current assets	308,819	178,222
Non-current assets:	'	'
Property and equipment, net	3,282	3,372
Deferred tax assets, non-current	1,496	816
Total non-current assets	4,778	4,188
Total assets	313,597	182,410
Current liabilities:	'	'
Accounts payable	1,240	1,790
Accrued research and development	4,635	1,542
Income taxes payable	282	184
Other current liabilities	3,814	3,890
Total current liabilities	9,971	7,406
Non-current liabilities:	'	'
Income taxes payable, non-current	28	0
Deferred rent	2,037	1,734
Total non-current liabilities	2,065	1,734
Total liabilities	12,036	9,140
Commitments and contingencies (Note 6)	'	'
Shareholders’ equity:	'	'
Euro deferred shares, €22 nominal value: Authorized shares - 10,000 at September 30, 2014 and December 31, 2013 Issued and outstanding shares - none at September 30, 2014 and December 31, 2013	0	0
Ordinary shares, $0.01 par value: Authorized shares - 100,000,000 at September 30, 2014 and December 31, 2013 Issued and outstanding shares - 27,381,624 and 21,856,261 at September 30, 2014 and December 31, 2013	274	219
Additional paid-in capital	336,668	214,392
Accumulated deficit	-35,381	-41,341
Total shareholders’ equity	301,561	173,270
Total liabilities and shareholders’ equity	$313,597	$182,410

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical)	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2013
	USD ($)	EUR (€)	USD ($)	EUR (€)
Statement of Financial Position [Abstract]	'	'	'	'
Euro deferred shares, nominal value (in euros per share)	'	€ 22	'	€ 22
Euro deferred shares, number of shares authorized	10,000	10,000	10,000	10,000
Euro deferred shares, number of issued shares	0	0	0	0
Euro deferred shares, number of outstanding shares	0	0	0	0
Ordinary shares, par value (in dollars per share)	$0.01	'	$0.01	'
Ordinary shares, number of authorized shares	100,000,000	100,000,000	100,000,000	100,000,000
Ordinary shares, number of issued shares	27,381,624	27,381,624	21,856,261	21,856,261
Ordinary shares, number of outstanding shares	27,381,624	27,381,624	21,856,261	21,856,261

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Operations (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Collaboration revenue	$1,349	$0	$48,429	$0
Revenue—related party	137	171	412	509
Total revenue	1,486	171	48,841	509
Operating expenses:	'	'	'	'
Research and development	10,388	6,348	28,345	20,452
General and administrative	4,230	3,389	14,040	9,782
Total operating expenses	14,618	9,737	42,385	30,234
Income (loss) from operations	-13,132	-9,566	6,456	-29,725
Other income (expense):	'	'	'	'
Interest income	19	14	54	50
Other income, net	172	0	138	0
Total other income	191	14	192	50
Income (loss) before income taxes	-12,941	-9,552	6,648	-29,675
Provision for income taxes	241	137	688	267
Net income (loss)	($13,182)	($9,689)	$5,960	($29,942)
Net income (loss) per share attributable to holders of ordinary shares	'	'	'	'
Basic (in dollars per share)	($0.48)	($0.55)	$0.25	($1.69)
Diluted (in dollars per share)	($0.48)	($0.55)	$0.24	($1.69)
Shares used to compute net income (loss) per share attributable to holders of ordinary shares	'	'	'	'
Basic (in shares)	27,370	17,679	23,758	17,679
Diluted (in shares)	27,370	17,679	24,722	17,679

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Operating activities	'	'
Net income (loss)	$5,960	($29,942)
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:	'	'
Depreciation and amortization	549	428
Share-based compensation	4,199	2,037
Excess tax benefit from share-based award exercises	-262	0
Deferred income taxes	-688	-586
Gain on disposal of fixed asset	0	-29
Changes in operating assets and liabilities:	'	'
Receivable from Roche	-967	0
Receivable from related party	-34	169
Other assets	-112	-73
Accounts payable, accruals and other liabilities	3,195	5,734
Net cash provided by (used in) operating activities	11,840	-22,262
Investing activities	'	'
Purchases of property and equipment	-459	-567
Proceeds from disposal of fixed asset	0	29
Net cash used in investing activities	-459	-538
Financing activities	'	'
Post separation adjustments to the funding provided by Elan	0	-84
Proceeds from issuance of ordinary shares upon exercise of stock options	442	0
Excess tax benefit from share-based award exercises	262	0
Cash paid for deferred offering costs	0	-117
Proceeds from issuance of ordinary shares in public offering, net	117,391	0
Net cash provided by (used in) financing activities	118,095	-201
Net increase (decrease) in cash and cash equivalents	129,476	-23,001
Cash and cash equivalents, beginning of the year	176,677	124,860
Cash and cash equivalents, end of the period	306,153	101,859
Supplemental disclosures of cash flow information	'	'
Cash paid for income taxes, net of refunds	988	263
Supplemental disclosures of non-cash investing and financing activities	'	'
Offering costs in accounts payable and accrued liabilities	$45	$0

Organization

Organization	9 Months Ended
	Sep. 30, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Organization	'
	Organization
	Description of Business
	Prothena Corporation plc and its subsidiaries (“Prothena” or the “Company”) is a clinical stage biotechnology company focused on the discovery, development and commercialization of novel antibodies for the potential treatment of diseases that involve protein misfolding or cell adhesion. The Company is focused on therapeutic monoclonal antibodies directed specifically to disease causing proteins. The Company's antibody-based product candidates target a number of potential indications including AL and AA forms of amyloidosis (NEOD001), Parkinson’s disease and other related synucleinopathies (PRX002) and novel cell adhesion targets involved in psoriasis and other inflammatory diseases (PRX003). The Company's strategy is to identify antibody candidates for clinical development by applying its extensive expertise in generating novel therapeutic antibodies and working with collaborators having expertise in specific animal models of disease.
	The Company is a public limited company formed under the laws of Ireland. The Company separated from Elan Corporation Limited, formerly Elan Corporation, plc (“Elan”), which was subsequently acquired by Perrigo Company plc (“Perrigo”), on December 20, 2012. Prothena's business consists of a substantial portion of Elan's former drug discovery business platform, including Neotope Biosciences Limited and its wholly owned subsidiaries Onclave Therapeutics Limited and Prothena Biosciences Inc (which for the period prior to separation and distribution are collectively referred to herein as the “Prothena Business”). Prior to December 21, 2012, the Prothena Business operated as part of Elan and not as a separate stand-alone entity. After the separation from Elan, and the related distribution of the Company's ordinary shares to Elan’s shareholders (the “Separation and Distribution”), the Company's ordinary shares commenced 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, 2014, the Company had an accumulated deficit of $35.4 million and cash and cash equivalents of $306.2 million.
	In February 2014, the Company received $30.0 million upfront payment pursuant to a License, Development, and Commercialization Agreement (the "License Agreement") with F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (collectively, "Roche"). In addition, in May 2014 the Company received a $15.0 million payment from Roche upon achievement of a clinical milestone related to the initiation of the Phase 1 study for PRX002 in April 2014.
	In June and July 2014, the Company sold an aggregate of 5,462,500 ordinary shares for net proceeds of approximately $117.4 million, after deducting the underwriting discount and estimated offering expenses, in an underwritten public offering.
	Based on the Company's business plans, management believes that the Company's cash and cash equivalents at September 30, 2014 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 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 collaboration with Roche, 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.
	The Company is dependent on Boehringer Ingelheim to manufacture clinical supplies for its therapeutic antibody programs. An inability to obtain product supply on a timely basis could have a material adverse impact on the Company's business, financial condition and results of operations.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	Summary of Significant Accounting Policies
	Basis of Preparation and Presentation of Financial Information
	The accompanying interim Condensed Consolidated Financial Statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (“GAAP”) and with the instructions for Form 10-Q and Regulation S-X. Accordingly, they do not include all of the information and notes required for complete financial statements. These interim Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes thereto contained in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (“SEC”) on March 7, 2014 (the "2013 Form 10-K"). The Condensed Consolidated Financial Statements of Prothena Corporation plc are presented in U.S. dollars, which is the functional currency of the Company. The unaudited condensed consolidated financial statements include the accounts of the Company and its consolidated subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
	Unaudited Interim Financial Information
	The accompanying interim Condensed Consolidated Financial Statements and related disclosures are unaudited, have been prepared on the same basis as the annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for a fair presentation of the results of operations for the periods presented. The year-end condensed balance sheet data was derived from audited financial statements, but does not include all disclosures required by GAAP. The condensed consolidated results of operations for any interim period are not necessarily indicative of the results to be expected for the full year or for any other future year or interim period. Although we achieved net income in the first nine months of 2014, primarily as a result of the $30.0 million upfront payment and the $15.0 million milestone payment under the Roche License Agreement, we expect to incur substantial losses for the foreseeable future.
	Use of Estimates
	The preparation of the Condensed Consolidated Financial Statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses. Because of the uncertainties inherent in such estimates, actual results may differ materially from these estimates.
	Significant Accounting Policies
	There have been no material changes to the significant accounting policies during the nine months ended September 30, 2014, as compared to the significant accounting policies described in Note 2 of the “Notes to Consolidated Financial Statements” in the 2013 Form 10-K, other than those listed below.
	Revenue Recognition
	Revenue is recognized when earned and non-refundable, when payment is reasonably assured, and when there is no future obligation with respect to the revenue, in accordance with the terms prescribed in the applicable contract.
	Multiple Element Arrangements
	The Company's revenues are generated primarily through its license, development and commercialization agreement. These types of agreements generally contain multiple elements, or deliverables, which may include (i) licenses to the Company's technology, (ii) R&D activities to be performed on behalf of the collaborative partner, and (iii) in certain cases, services or obligations in connection with the manufacturing or supply of pre-clinical and clinical material. Payments to the Company under these arrangements typically include one or more of the following: non-refundable, upfront license fees; funding of research and/or development efforts; milestone payments; and royalties on future product sales.
	Revenue under license, development and commercialization agreements is recognized based on the performance requirements of the contract. Determinations of whether persuasive evidence of an arrangement exists and whether delivery has occurred or services have been rendered are based on management’s judgments regarding the fixed nature of the fees charged for deliverables and the collectability of those fees.
	The Company recognizes revenue related to license, development and commercialization agreements in accordance with the provisions of Financial Accounting Standards Board, or FASB, Accounting Standards Codification, or ASC, Topic 605-25, “Revenue Recognition - Multiple-Element Arrangements.” The Company evaluates all deliverables within an arrangement to determine whether or not they provide value on a stand-alone basis. Based on this evaluation, the deliverables are separated into units of accounting. The arrangement consideration that is fixed or determinable at the inception of the arrangement is allocated to the separate units of accounting based on their relative selling prices.
	To determine the selling price of a separate deliverable, the Company uses the hierarchy as prescribed in ASC Topic 605-25 based on vendor-specific objective evidence (VSOE), third-party evidence (TPE) or best estimate of selling price (BESP). VSOE is based on the price charged when the element is sold separately and is the price actually charged for that deliverable. TPE is determined based on third party evidence for a similar deliverable when sold separately and BESP is the estimated selling price at which we would transact a sale if the elements of collaboration and license arrangements were sold on a stand-alone basis to the buyer.
	Payments or full reimbursements resulting from our R&D efforts for those arrangements where such efforts are considered as deliverables are recognized as the services are performed and are presented on a gross basis so long as there is persuasive evidence of an arrangement, the fee is fixed or determinable, and collection of the related receivable is reasonably assured. However, such funding is recognized as a reduction of R&D expense when the Company engages in a R&D project jointly with another entity, with both entities participating in project activities and sharing costs and potential benefits of the project.
	Milestone Revenue
	The Company accounts for milestones under ASU No. 2010-17, Milestone Method of Revenue Recognition. Under the milestone method, contingent consideration received from the achievement of a substantive milestone is recognized in its entirety in the period in which the milestone is achieved. A milestone is defined as an event (i) that can only be achieved based in whole or in part on either the entity’s performance or on the occurrence of a specific outcome resulting from the entity’s performance, (ii) for which there is substantive uncertainty at the date the arrangement is entered into that the event will be achieved, and (iii) that would result in additional payments being due to the entity. At the inception of an agreement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether (a) the consideration is commensurate with either (1) the entity’s performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the entity’s performance to achieve the milestone, (b) the consideration relates solely to past performance, and (c) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve a particular milestone, the level of effort and investment required to achieve such milestone and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement in making this assessment.
	The Company generally classifies each of its milestones into one of three categories: (i) clinical milestones, (ii) regulatory and development milestones, and (iii) commercial milestones. Clinical milestones are typically achieved when a product candidate advances into or completes a defined phase of clinical research. For example, a milestone payment may be due to the Company upon the initiation of a clinical trial for a new indication. Regulatory and development milestones are typically achieved upon acceptance of the submission for marketing approval of a product candidate or upon approval to market the product candidate by the U.S. Food and Drug Administration (the "FDA") or other regulatory authorities. For example, a milestone payment may be due to the Company upon filing of a Biologics License Application (BLA) with the FDA. Commercial milestones are typically achieved when an approved pharmaceutical product reaches certain defined levels of net royalty sales by the licensee of a specified amount within a specified period.
	Commercial milestone payments and milestone payments that are not deemed to be substantive will be accounted for as a contingent revenue payment with revenue recognized when all contingencies are lifted, which is expected to be upon achievement of the milestone, assuming all revenue recognition criteria are met.
	Profit Share Revenue
	For agreements, with profit sharing arrangements, the Company will record its share of the pre-tax commercial profit as collaboration revenue when the profit sharing can be reasonably estimated and collectability is reasonably assured.
	Royalty Revenue
	The Company will recognize revenue from royalties based on licensees' sales of the Company's products or products using the Company's technologies. Royalties are recognized as earned in accordance with the contract terms when royalties from licensees can be reasonably estimated and collectability is reasonably assured.
	Net Income per Ordinary Share
	Basic net income (loss) per ordinary share is computed by dividing net income (loss) attributable to ordinary shareholders by the weighted average number of ordinary shares outstanding during the period less the weighted average number of unvested restricted ordinary shares subject to the right of repurchase. Diluted net income per ordinary share is computed by giving effect to all dilutive potential ordinary shares including options. However, potentially issuable ordinary shares are not used in computing diluted net loss per ordinary share as their effect would be anti-dilutive due to the loss recorded.
	Comprehensive Income (Loss)
	Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income (loss). The Company has no components of other comprehensive income (loss). Therefore net income (loss) equals comprehensive income (loss) for all periods presented and, accordingly, the Condensed Consolidated Statements of Comprehensive Income (Loss) is not presented in a separate statement.
	Segment and Concentration of Risks
	The Company operates one segment. The Company’s chief operating decision maker (the “CODM”), its Chief Executive Officer, manages the Company’s operations on a consolidated basis for purposes of allocating resources. When evaluating the Company’s financial performance, the CODM reviews all financial information on a consolidated basis.
	Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents and accounts receivable. The Company places its cash equivalents with high credit quality financial institutions and by policy, limits the amount of credit exposure with any one financial institution. Deposits held with banks may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits of cash and cash equivalents and its credit risk exposure is up to the extent recorded on the Company's consolidated balance sheet.
	All of the Company's long-lived assets were held in the U.S. The Company’s accounts receivable from related party are from Elan located in Ireland for all periods presented. For the three and nine months ended September 30, 2014, receivable from Roche includes amounts due from Roche entities located in the U.S. and Switzerland under the License Agreement that became effective January 22, 2014. Revenue recorded in the Statements of Operations consists of collaboration revenue related to the upfront payment from Roche under the License Agreement, payment from Roche upon achievement of a clinical milestone and reimbursement for research and development services and fees earned from the provision of nonclinical research support to Elan, primarily in the areas of safety, toxicology and regulatory. The fees charged to Elan were calculated based on the expenses incurred by the Company in the provision of those R&D services, plus a contractually determined mark-up of those expenses.
	The Company utilizes Boehringer Ingelheim in Switzerland for its clinical drug product supply for therapeutic antibody programs. An inability to obtain drug product supply on a timely basis could have a material adverse impact on the Company's business, financial condition and results of operations.
	Emerging Growth Company Status
	As an Emerging Growth Company under the Jumpstart Our Business Startups Act (“JOBS Act”), the Company is eligible to take advantage of certain exemptions from various reporting requirements that apply to other public companies that are not Emerging Growth Companies. The Company has an extended transition period for adopting new or revised accounting standards that have different effective dates for public and private companies until such time as those standards apply to private companies.
	Recent Accounting Pronouncements
	Except for the standards below, there have been no new accounting pronouncements or changes to accounting pronouncements during the nine months ended September 30, 2014, as compared to the recent accounting pronouncements described in our 2013 Form 10-K, that are of significance or potential significance to the Company.
	In May 2014, the FASB issued Accounting Standards Update 2014-09 (ASU 2014-09), Revenue from Contracts with Customers. ASU 2014-09 supersedes the revenue recognition requirements in Revenue Recognition (Topic 605), and requires entities to recognize revenue in a way that depicts the transfer of promised goods and services to customers in an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services. ASU 2014-09 is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period, which for the Company is January 1, 2017. Early adoption is not permitted. The standard permits the use of either retrospective or cumulative effect transition method. The Company is currently evaluating the potential impact the adoption of ASU 2014-09 will have on its consolidated financial statements. The Company has not yet selected a transition method nor has it determined the effect of the standard on its ongoing financial reporting.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	The Company measures certain financial assets and liabilities at fair value on a recurring basis, including cash equivalents. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. A three-tier fair value hierarchy is established as a basis for considering such assumptions and for inputs used in the valuation methodologies in measuring fair value:
	Level 1 —    Observable inputs such as quoted prices (unadjusted) for identical assets or liabilities in active markets.
	Level 2 —	Include other inputs that are based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuation techniques for which all significant inputs are observable in the market or can be derived from observable market data. Where applicable, these models project future cash flows and discount the future amounts to a present value using market-based observable inputs including interest rate curves, foreign exchange rates, and credit ratings.
	Level 3 —	Unobservable inputs that are supported by little or no market activities, which would require the Company to develop its own assumptions.
	The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The carrying amounts of certain financial instruments, such as cash equivalents, accounts receivable, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities, and low market interest rates, if applicable.
	Based on the fair value hierarchy, the Company classifies its cash equivalents within Level 1. This is because the Company values its cash equivalents using quoted market prices. The Company’s Level 1 securities consist of $275.1 million and $153.3 million in money market funds included in cash and cash equivalents at September 30, 2014 and December 31, 2013, respectively.

Composition_of_Certain_Balance

Composition of Certain Balance Sheet Items	9 Months Ended
	Sep. 30, 2014
Composition of Certain Balance Sheet Items [Abstract]	'
Composition of Certain Balance Sheet Items	'
	Composition of Certain Balance Sheet Items
	Property and Equipment, net
	Property and equipment, net consisted of the following (in thousands):
		September 30,			December 31,
		2014			2013
	Machinery and equipment	$	5,789		$	5,649
	Leasehold improvements	2,211			1,927
	Purchased computer software	120			85
		8,120			7,661
	Less: accumulated depreciation and amortization	(4,838		)	(4,289		)
	Property and equipment, net	$	3,282		$	3,372
	Depreciation and amortization expense was $0.2 million and $0.5 million for the three and nine months ended September 30, 2014 compared to $0.1 million and $0.4 million for the three and nine months ended September 30, 2013, respectively.
	Other Current Liabilities
	Other current liabilities consisted of the following (in thousands):
		September 30,			December 31,
		2014			2013
	Payroll and related expenses	$	2,315		$	2,800
	Professional services	984			616
	Accrued offering costs	31			82
	Deferred rent	138			138
	Other	346			254
	Other current liabilities	$	3,814		$	3,890

Net_income_loss_Per_Ordinary_S

Net income (loss) Per Ordinary Share	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Net income (loss) Per Ordinary Share	'
	Net Income (Loss) Per Ordinary Share
	Basic net income (loss) per ordinary share is calculated by dividing net income (loss) by the weighted-average number of ordinary shares outstanding during the period. Shares used in diluted net income (loss) per ordinary share would include the dilutive effect of ordinary shares potentially issuable upon the exercise of stock options outstanding and restricted stock units. However, potentially issuable ordinary shares are not used in computing diluted net loss per ordinary share as their effect would be anti-dilutive due to the loss recorded during the three months ended September 30, 2014 and 2013 and nine months ended September 30, 2013, and therefore diluted net loss per ordinary share is equal to basic net loss per ordinary share. During the nine months ended September 30, 2014, diluted net income per ordinary share is computed by giving effect to all dilutive potential ordinary shares including options.
	Net income (loss) per ordinary share was determined as follows (in thousands, except per share amounts):
			Three Months Ended September 30,						Nine Months Ended
									September 30,
			2014			2013			2014		2013
	Numerator (basic and dilutive):
	Net income (loss)		$	(13,182	)	$	(9,689	)	$	5,960	$	(29,942	)
	Denominator (basic):
	Weighted-average ordinary shares outstanding		27,370			17,679			23,758		17,679
	Denominator (diluted):
	Weighted-average ordinary shares outstanding		27,370			17,679			23,758		17,679
	Dilutive stock options outstanding		—			—			964		—
	Net weighted average ordinary shares outstanding		27,370			17,679			24,722		17,679
	Net income (loss) per share attributable to holders of ordinary shares:
	Basic net income (loss) per share		$	(0.48	)	$	(0.55	)	$	0.25	$	(1.69	)
	Diluted net income (loss) per share		$	(0.48	)	$	(0.55	)	$	0.24	$	(1.69	)
	The equivalent ordinary shares not included in diluted net income (loss) per share because their effect would be anti-dilutive are as follows (in thousands):
		Three Months Ended September 30,					Nine Months Ended
							September 30,
		2014			2013		2014		2013
	Options to purchase ordinary shares	777			57		632		76
	Total	777			57		632		76

Commitment_and_Contingencies

Commitment and Contingencies	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitment and Contingencies	'
	Commitments and Contingencies
	Operating Lease
	The Company has a noncancelable operating lease agreement for office and research and development space in the U.S. that expires in November 2020 with an estimated annual rent payment of approximately $1.9 million. The lease provides for approximately 50,400 of rentable square feet at a base rent that increases annually.
	Future minimum payments under operating leases as of September 30, 2014, are as follows (in thousands):
	Year Ended December 31,		Operating Lease
	2014 (Remaining 3 months)		$	368
	2015		1,834
	2016		1,938
	2017		2,017
	2018		2,096
	Thereafter		4,237
	Total future minimum lease payments		$	12,490
	The Company recognizes rent expense on a straight-line basis over the noncancelable lease term and records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Where leases contain escalation clauses, rent abatements, and/or concessions, such as rent holidays and landlord or tenant incentives or allowances, the Company applies them in the determination of straight-line rent expense over the lease term. The Company records the tenant improvement allowance as deferred rent and associated expenditures as leasehold improvements that are being amortized over the shorter of their estimated useful life or the term of the lease. Rent expense was $0.5 million and $0.3 million for the three months ended September 30, 2014 and 2013, respectively, and $1.3 million and $0.9 million for the nine months ended September 30, 2014 and 2013, respectively.
	Indemnity Obligations
	The Company has entered into indemnification agreements with its current, and former, directors and officers and certain key employees. These agreements contain provisions that may require the Company, among other things, to indemnify such persons against certain liabilities that may arise because of their status or service and advance their expenses incurred as a result of any indemnifiable proceedings brought against them. The obligations of the Company pursuant to the indemnification agreements continue during such time as the indemnified person serves the Company and continues thereafter until such time as a claim can be brought. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited; however, the Company has a director and officer insurance policy that limits its exposure and enables the Company to recover a portion of any future amounts paid. As a result of its insurance policy coverage, the Company believes the estimated fair value of these indemnification agreements is minimal. Accordingly, the Company had no liabilities recorded for these agreements as of September 30, 2014 and 2013.
	Commitments
	As of September 30, 2014, the Company had non-cancelable purchase commitments to suppliers for $3.2 million of which $3.0 million is included in accrued current liabilities, and contractual obligations under license agreements of $1.2 million of which less than $0.1 million is included in accrued current liabilities. The following is a summary of the Company's non-cancelable purchase commitments and contractual obligations as of September 30, 2014 (in thousands):
		Total			2014		2015		2016		2017		2018		Thereafter
					(Remaining 3 months)
	Purchase Obligations	$	3,170		$	3,170	$	—	$	—	$	—	$	—	$	—
	Contractual obligations under license agreements (1)	1,225			135		100		100		100		100		690
	Total	$	4,395		$	3,305	$	100	$	100	$	100	$	100	$	690
	(1) Excludes future obligations pursuant to the cost-sharing arrangement under the Company's License Agreement with Roche. Amounts of such obligations, if any, cannot be determined at this time.

Significant_Agreements

Significant Agreements	9 Months Ended
	Sep. 30, 2014
Collaborative Agreement [Abstract]	'
Significant Agreements	'
	Roche License Agreement
	Overview
	In December 2013, the Company entered into the License Agreement with Roche to develop and commercialize certain antibodies that target alpha-synuclein, including PRX002, which are referred to collectively as “Licensed Products.” On January 22, 2014 the License Agreement with Roche became effective following the expiration of the Hart-Scott-Rodino (HSR) waiting period. Upon the effectiveness of the License Agreement, the Company granted to Roche an exclusive, worldwide license to develop, make, have made, use, sell, offer to sell, import, and export the Licensed Products. The Company retained certain rights to conduct development of the Licensed Products and an option to co-promote PRX002 in the U.S. During the term of the License Agreement, the Company and Roche will work exclusively with each other to research and develop antibody products targeting alpha-synuclein potentially including incorporation of Roche’s proprietary Brain Shuttle™ technology to potentially increase delivery of therapeutic antibodies to the brain. The License Agreement provides that Roche would make an upfront payment to the Company of $30.0 million, which was received in February 2014, and the clinical milestone payment of $15.0 million triggered by the initiation of the Phase 1 study for PRX002 in the clinic, which was received in May 2014.
	For PRX002, Roche is also obligated to pay:
	• up to $380.0 million upon the achievement of development, regulatory and various first commercial sales milestones;
	• up to an additional $175.0 million in ex-U.S. commercial sales milestones; and
	• tiered, high single-digit to high double-digit royalties in the teens on ex-U.S. annual net sales, subject to certain adjustments.
	Roche bears 100% of the cost of conducting the research activities under the License Agreement. In the U.S., the parties will share all development and commercialization costs, as well as profits, all of which will be allocated 70% to Roche and 30% to the Company, for PRX002 in the Parkinson’s disease indication, as well as any other Licensed Products and/or indications for which the Company opts in to participate in co-development and co-funding. After the completion of specific clinical trial activities, the Company may opt out of the co-development and cost and profit sharing on any co-developed Licensed Products and instead receive U.S. commercial sales milestones totaling up to $155.0 million and tiered, single-digit to high double-digit royalties in the teens based on U.S. annual net sales, subject to certain adjustments, with respect to the applicable Licensed Product.
	The Company filed an investigational new drug ("IND") application with the U.S. Food and Drug Administration for PRX002 and subsequently initiated a Phase 1 study in 2014. Following the Phase 1 study, Roche will be primarily responsible for developing, obtaining and maintaining regulatory approval for, and commercializing Licensed Products. Roche will also become responsible for the clinical and commercial manufacture and supply of Licensed Products within a defined time period following the effective date of the License Agreement.
	In addition, the Company has an option under the License Agreement to co-promote PRX002 in the U.S. in the Parkinson’s disease indication. If the Company exercises such option, it may also elect to co-promote additional Licensed Products in the U.S. approved for Parkinson’s disease. Outside the U.S., Roche will have responsibility for developing and commercializing the Licensed Products. Roche bears all costs that are specifically related to obtaining or maintaining regulatory approval outside the U.S. and will pay the Company a variable royalty based on annual net sales of the Licensed Products outside the U.S.
	While Roche will record product revenue from sales of the Licensed Products, the Company and Roche will share in the net profits and losses of sales of the PRX002 for the Parkinson's disease indication in the U.S. on a 70%/30% basis with the Company receiving 30% of the profit and losses provided that the Company has not exercised its opt-out right.
	The License Agreement continues on a country-by-country basis until the expiration of all payment obligations under the License Agreement. The License Agreement may also be terminated (i) by Roche at will after the first anniversary of the effective date of the License Agreement, either in its entirety or on a Licensed Product-by-Licensed Product basis, upon 90 days’ prior written notice to the Company prior to first commercial sale and 180 days’ prior written notice to Prothena after first commercial sale, (ii) by either party, either in its entirety or on a Licensed Product-by-Licensed Product or region-by-region basis, upon written notice in connection with a material breach uncured 90 days after initial written notice, and (iii) by either party, in its entirety, upon insolvency of the other party. The License Agreement may be terminated by either party on a patent-by-patent and country-by-country basis if the other party challenges a given patent in a given country. The Company’s rights to co-develop Licensed Products under the License Agreement will terminate if the Company commences certain studies for certain types of competitive products. The Company’s rights to co-promote Licensed Products under the License Agreement will terminate if the Company commences a Phase 3 study for such competitive products.
	The License Agreement cannot be assigned by either party without the prior written consent of the other party, except to an affiliate of such party or in the event of a merger or acquisition of such party, subject to certain conditions. The License Agreement also includes customary provisions regarding, among other things, confidentiality, intellectual property ownership, patent prosecution, enforcement and defense, representations and warranties, indemnification, insurance, and arbitration and dispute resolution.
	Collaboration Accounting
	The License Agreement was evaluated under ASC 808, Collaborative Agreements. At the outset of the contract, the Company concluded that this agreement does not qualify as a collaboration under ASC 808 because Prothena is not an active participant as a result of the opt-out provision. The Company believes that Roche is the principal in the sales transactions with third parties as it is the primary obligor, bearing inventory and credit risk. The Company will record its share of pre-tax commercial profit generated from the collaboration with Roche, as collaboration revenue when the profit share can be reasonably estimated and collectability is reasonably assured. Prior to commercialization of a Licensed Product, the Company's portion of the expenses related to the License Agreement reflected on its income statement will be limited to R&D expenses. After commercialization, if the Company opts-in to co-detail commercialization expenses related to commercial capabilities, including the establishment of a field sales force and other activities to support the Company’s commercialization efforts, will be recorded as SG&A expense and will be factored into the computation of the profit and loss share. The Company will record the portion of the net receivable related to commercialization activities as collaboration revenue.
	Multiple Element Accounting
	The License Agreement was evaluated under ASC 605-25, Multiple Element Arrangements. The License Agreement includes the following deliverables: (1) an exclusive royalty bearing license, with the right to sublicense to develop and commercialize certain antibodies that target alpha-synuclein, including PRX002 delivered at the effective date; (2) the Company's obligation to supply clinical material as requested by Roche for a period up to twelve months; (3) the Company's obligation to provide manufacturing related services to Roche for a period up to twelve months; (4) the Company's obligation to provide development activities under the development plan including the preparation and filing of the IND and initiation of the Phase I clinical trial estimated to be carried out over the next two years; and (5) the Company's obligation to provide indeterminate research services for up to three years at rates that are not significantly discounted and fully reimbursable by Roche.
	All of the deliverables were deemed to have stand-alone value and to meet the criteria to be accounted for as separate units of accounting under ASC 605-25. Factors considered in the determination included, among other things, for the license, the research and development capabilities of Roche and Roche’s sublicense rights, and for the remaining deliverables the fact that they are not proprietary and can be and have been provided by other vendors.
	The amount of allocable arrangement consideration is limited to amounts that are fixed or determinable excluding refund rights, concessions or performance bonuses. As such, the Company will exclude from such allocable consideration the milestone payments and royalties regardless of the probability of receipt because such payments are not considered fixed or determinable. Such milestone payments and royalties will be evaluated separately as the related contingencies are resolved. Consideration for research services were not allocated as the amount is not fixed and determinable and is not at a significant incremental discount. There are no refund rights, concessions or performance bonuses to consider.
	The Company allocated the fixed and determinable consideration to the license and other deliverables using the relative selling price method based on the best estimate of selling price for the license and third party evidence for the remaining deliverables. The best estimate of selling price for the license was based on a discounted cash flow model. The key assumptions used in the discounted cash flow model used to determine the best estimate of selling price for the license granted to Roche under the License Agreement included the market opportunity for commercialization of PRX002 in the U.S. and the Royalty Territory (for jointly funded products the Royalty Territory is worldwide except for the U.S. for all Licensed Products that are not jointly funded the Royalty Territory is worldwide), the probability of successfully developing and commercializing PRX002, the remaining development costs for PRX002, and the estimated time to commercialization of PRX002.
	The Company’s discounted cash flow model included several market conditions and entity-specific inputs, including the likelihood that clinical trials will be successful, the likelihood that regulatory approval will be obtained and the product commercialized, the appropriate discount rate, the market locations, size and potential market share of the product, the expected life of the product, and the competitive environment for the product. The market assumptions were generated using a patient-based forecasting approach, with key epidemiological, market penetration, dosing, compliance, length of treatment, and pricing assumptions derived from primary and secondary market research, referenced from third-party sources.
	The Company concluded that a change in the assumptions used to determine the BESP of the license deliverable would not have a significant effect on the allocation of arrangement consideration. Based on the relative selling price method, the amount that the Company recognized on the effective date of the agreement concurrent with the delivery of the license and know-how was limited to the lesser of the amount otherwise allocable using the relative selling price method, which based on the discounted cash flow model was determined to be $34.7 million, or the non-contingent amount which was the $30.0 million upfront fee. In the quarter ended June 30, 2014, the Company updated the relative sales price model to include overhead allocation and contractually stated administrative fee for development services, which resulted in a change to allocated consideration for the license from $34.7 million to $35.6 million. As the remaining deliverables are delivered, any consideration received will be allocated to license revenue and the other deliverables based on their relative percentages until such time as the full allocated consideration of $35.6 million has been recognized as license revenue, and the balance of the monetary consideration will be recorded as an offset against R&D expenses. The Company recognized the $30.0 million upfront payment as collaboration license revenue in the first quarter of 2014.
	The Company recognizes the research reimbursement as collaboration revenue as earned. The Company recognized $0.4 million and $1.1 million as collaboration service revenue during the three and nine months ended September 30, 2014, respectively, for research reimbursement from Roche. Cost sharing payments to Roche will be recorded as R&D expenses. The Company recognized $0.5 million and $1.0 million in R&D expense for payments made to Roche during the three and nine months ended September 30, 2014, respectively. Reimbursement for development costs from Roche under the cost-sharing arrangement will be allocated between license revenue and an offset to R&D expenses based on the relative selling price method until the full allocated consideration of $35.6 million has been recognized as license revenue, after which the full reimbursement would be recorded as an offset to R&D expenses. Reimbursement for development costs from Roche during the three and nine months ended September 30, 2014 were $1.0 million, and $4.5 million, respectively, of which $0.9 million and $4.0 million, respectively, were recognized as collaboration license revenue and $0.1 million and $0.5 million, respectively, were recognized as an offset to R&D expenses.
	Milestone Accounting
	In April 2014, the Company together with Roche initiated a Phase 1 clinical trial of PRX002. As a result of this initiation, the Company received a $15.0 million milestone payment from Roche under the License Agreement. The Company concluded that the $15.0 million clinical milestone triggered upon the initiation of the Phase 1 study from PRX002 in the clinic is consistent with the definition of a substantive milestone included in ASU No. 2010-17, Milestone Method of Revenue Recognition. Factors considered in this determination included scientific and regulatory risk that must be overcome to achieve each milestone, the level of effort and investment required to achieve the milestone, and the monetary value attributed to the milestone.
	Accordingly, the Company recognized payments related to the achievement of this milestone when the milestone was achieved. The milestone payment was allocated to the units of accounting based on the relative selling price method for income statement classification purposes. In the three months ended June 30, 2014, the Company recognized $13.3 million of the $15.0 million milestone payment as collaboration revenue and $1.7 million as an offset to R&D expenses.
	The clinical and regulatory milestones under the License Agreement after the point at which the Company could opt-out are not considered to be substantive due to the fact that active participation in the development actives that generate the milestones is not required by the License Agreement, and the Company can opt-out of these activities. There are no refund or claw-back provisions and the milestones are uncertain of occurrence even after the Company has opted out. Based on this determination, these milestones will be recognized similar to the commercial milestone, which will be accounted for as contingent revenue payments with revenue recognized upon achievement of the milestone assuming all revenue recognition criteria are met. The Company did not achieve any of these other clinical and regulatory milestones under the License Agreement during the three and nine months ended September 30, 2014.

Shareholders_Equity

Shareholder's Equity	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Shareholder's Equity	'
	Shareholders' Equity
	Ordinary Shares
	As of September 30, 2014, the Company had 100,000,000 ordinary shares authorized for issuance with a par value of $0.01 per ordinary share and 27,381,624 ordinary shares issued and outstanding. Each ordinary share is entitled to one vote and, on a pro rata basis, to dividends when declared and the remaining assets of the Company in the event of a winding up.
	Euro Deferred Shares
	As of September 30, 2014, the Company had 10,000 Euro Deferred Shares authorized for issuance with a nominal value of €22 per share. No Euro Deferred Shares are outstanding at September 30, 2014. The rights and restrictions attaching to the Euro Deferred Shares rank pari passu with the ordinary shares and are treated as a single class in all respects.
	February 2014 Offering
	In February 2014 Elan Science One Limited, or ESOL, an indirect wholly owned subsidiary of Perrigo Company plc, or Perrigo, sold 3,182,253 ordinary shares of Prothena at a price to the public of $26.00 per ordinary share, before the underwriting discount. As a result, ESOL and Perrigo no longer own any ordinary shares of Prothena.
	The Company did not receive any of the proceeds from the offering, and the total number of the Company's ordinary shares outstanding did not change as a result of this offering. The Company paid the costs associated with the sale of these ordinary shares (other than the underwriting discount, fees and disbursements of counsel for the selling shareholder) pursuant to a Subscription and Registration Rights Agreement dated November 8, 2012 by and between the Company, Elan and ESOL.
	June 2014 Offering
	In June 2014 the Company completed an underwritten public offering of an aggregate of 4,750,000 of its ordinary shares at a public offering price of $22.50 per ordinary share. The Company received aggregate net proceeds of approximately $102.5 million, after deducting the underwriting discount and estimated offering costs.
	In connection with this offering, the Company granted the underwriters the right to subscribe for and purchase, as applicable, up to an additional 712,500 ordinary shares. In July 2014, the underwriters exercised such right to subscribe for and purchase an aggregate of 712,500 ordinary shares, pursuant to which the Company received net proceeds of approximately $14.9 million, after deducting the underwriting discount of approximately $1.1 million.
	For the three and nine months ended September 30, 2014, underwriting discount and offering expense of $1.2 million and $5.5 million, respectively, were classified as an offset to the proceeds and recorded in additional paid in capital on the balance sheet.

ShareBased_Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Share-Based Compensation	'
	Share-Based Compensation
	The Prothena Corporation plc Amended and Restated 2012 Long Term Incentive Plan (“LTIP”)
	Employees and consultants of the Company, its subsidiaries and affiliates, as well as members of the Board, are eligible to receive equity awards under the LTIP. The LTIP provides for the grant of stock options, including incentive stock options and nonqualified stock options, stock appreciation rights (“SARS”), restricted shares, restricted share units, cash or stock-based performance awards and other share-based awards to eligible individuals. Options under the LTIP may be granted for periods up to ten years. All options issued to date have had a ten year life. In March 2014, the Board amended the LTIP, which was subsequently approved by the shareholders on May 21, 2014 during the Company's Annual General Meeting of Shareholders. The Company's shareholders approved the increase in the aggregate number of ordinary shares authorized for issuance under the LTIP by 2,900,000 ordinary shares, to a total of 5,550,000 ordinary shares.
	The Company granted 47,500 and 99,000 share options during the three months ended September 30, 2014 and 2013, respectively, and 710,500 and 1,934,500 share options during the nine months ended September 30, 2014 and 2013, respectively, under the LTIP. The Company's option awards generally vest over four years. As of September 30, 2014, 2,866,000 ordinary shares remain available for grant and options to purchase 2,621,137 ordinary shares granted from the LTIP were outstanding with a weighted-average exercise price of approximately $13.10 per share.
	Prothena Share-based Compensation Expense
	The Company estimates the fair value of share-based compensation on the date of grant using an option-pricing model. The Company uses the Black-Scholes model to value share-based compensation, excluding RSUs, which the Company values using the fair market value of its ordinary shares on the date of grant. The Black-Scholes option-pricing model determines the fair value of share-based payment awards based on the share price on the date of grant and is affected by assumptions regarding a number of highly complex and subjective variables. These variables include, but are not limited to, the Company’s share price, volatility over the expected life of the awards and actual and projected employee stock option exercise behaviors. Since the Company has no historic employee share option exercise data, the simplified method has been used to estimate the expected life of all options. Although the fair value of share options granted by the Company is estimated by the Black-Scholes model, the estimated fair value may not be indicative of the fair value observed in a willing buyer and seller market transaction.
	As share-based compensation expense recognized in the Condensed Consolidated Financial Statements is based on awards ultimately expected to vest, it has been reduced for estimated forfeitures. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from estimates. Forfeitures were estimated based on estimated future turnover and historical experience.
	Share-based compensation expense will continue to have an adverse impact on the Company’s results of operations, although it will have no impact on its overall financial position. The amount of unearned share-based compensation currently estimated to be expensed from now through the year 2017 related to unvested share-based payment awards at September 30, 2014 is $17.4 million. The weighted-average period over which the unearned share-based compensation is expected to be recognized is 2.8 years. If there are any modifications or cancellations of the underlying unvested securities, the Company may be required to accelerate, increase or cancel any remaining unearned share-based compensation expense. Future share-based compensation expense and unearned share-based compensation will increase to the extent that the Company grants additional equity awards.
	Share-based compensation expense recorded in these Condensed Consolidated Financial Statements for the three and nine months ended September 30, 2014 and 2013 was based on awards granted under the LTIP. The following table summarizes share-based compensation expense for the periods presented (in thousands):
		Three Months Ended September 30,								Nine Months Ended
										September 30,
		2014				2013				2014				2013
	Research and development(1)	$	601			$	311			$	1,650			$	616
	General and administrative	817				644				2,549				1,421
	Total	$	1,418			$	955			$	4,199			$	2,037
	_________________
	(1)	Includes $20,000 and $108,000 for the three months ended September 30, 2014 and 2013, respectively, and $92,000 and $171,000 for the nine months ended September 30, 2014 and 2013, respectively, of share-based compensation expense related to options granted to a consultant.
	The fair value of the options granted to employees and non-employee directors during the three and nine months ended September 30, 2014 and 2013 is estimated as of the grant date using the Black-Scholes option-pricing model assuming the weighted-average assumptions listed in the following table:
			Three Months Ended September 30,				Nine Months Ended
							September 30,
			2014		2013		2014		2013
	Expected volatility		86.30%		81.00%		84.50%		84.10%
	Risk-free interest rate		1.90%		1.80%		1.80%		1.20%
	Expected dividend yield		—%		—%		—%		—%
	Expected life (in years)		6		6		6		6
	Weighted average grant date fair value		$15.01		$12.56		$20.03		$4.97
	The following table summarizes the Company’s share option activity during the nine months ended September 30, 2014:
		Options			Weighted				Weighted		Aggregate
					Average				Average		Intrinsic
					Exercise				Remaining		Value
					Price				Contractual		(in thousands)
									Term (years)
	Outstanding at December 31, 2013	1,973,500			$	7.5			9.17		$	37,528
	Granted	710,500			28.1
	Exercised	(62,863	)		7.05
	Canceled	—			—
	Outstanding at September 30, 2014	2,621,137			$	13.1			8.7		$	28,173
	Vested and expected to vest at September 30, 2014	2,528,276			$	12.95			8.69		$	27,461
	Vested at September 30, 2014	900,323			$	7.23			8.41		$	13,442
	The following table summarizes information about the Company's share options outstanding as of September 30, 2014:
								Options Outstanding								Options Exercisable
	Range of Exercise Prices							Number of Options			Weighted -		Weighted Average Exercise Price			Number of Options	Weighted Average Exercise Price
											Average
											Remaining
											Contractual Life
											(Years)
	$	6.03		$	6.03			453,375			8.33		$	6.03		188,250	$	6.03
	6.41			6.41				808,762			8.33		6.41			428,845	6.41
	6.65			6.65				50,000			8.46		6.65			50,000	6.65
	6.73			6.73				366,000			8.5		6.73			148,541	6.73
	8.21			22.14				346,500			9.14		17.26			84,687	15.26
	23.11			23.11				27,500			9.92		23.11			—	—
	24.26			24.26				30,000			9.09		24.26			—	—
	29.52			29.52				25,000			9.34		29.52			—	—
	29.81			29.81				484,000			9.35		29.81			—	—
	37.02			37.02				30,000			9.5		37.02			—	—
	$	6.03		$	37.02			2,621,137			8.7		$	13.1		900,323	$	7.23

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes
	The major taxing jurisdictions for the Company are Ireland and the U.S. The Company's income tax provision was $241,000 and $137,000 for the three months ended September 30, 2014 and 2013, respectively, and was $688,000 and $267,000 for the nine months ended September 30, 2014 and 2013, respectively. The provision for income taxes differs from the statutory tax rate of 12.5% applicable to Ireland primarily due to Irish net operating losses for which a tax provision benefit is not recognized and due to U.S. income taxed at different rates. Our income tax provision reflects our estimate of the effective tax rate expected to be applicable for the full year and we re-evaluate this estimate each quarter based on our forecasted tax expense for the full year. The effective income tax rate for the nine months ended September 30, 2014 does not include a benefit for the U.S. federal research credit as it has not been extended beyond 2013. Jurisdictions with a projected loss for the year where no tax benefit can be recognized are excluded from the estimated annual effective tax rate.
	The Company's deferred tax assets are composed primarily of its Irish subsidiaries' net operating loss carryovers, state net operating loss carryforwards available to reduce future taxable income of the Company's U.S. subsidiary, federal and state tax credit carryforwards and other temporary differences. We maintain a valuation allowance against certain U.S. federal and state and Irish deferred tax assets. Each reporting period, we evaluate the need for a valuation allowance on our deferred tax assets by jurisdiction.
	No provision for income tax in Ireland has been recognized on undistributed earnings of our foreign subsidiaries because we consider such earnings to be indefinitely reinvested.

Related_Parties

Related Parties	9 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Related Parties	'
	Related Parties
	Prior to December 21, 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 separation, a wholly owned subsidiary of Elan acquired an 18% interest in the Company (as calculated immediately following the separation). Elan was subsequently acquired by Perrigo Company plc, or Perrigo, in December 2013 and such 3,182,253 ordinary shares were held by Elan Science One Limited, or ESOL, an indirect wholly owned subsidiary of Perrigo as of December 31, 2013.
	February 2014 Offering
	In February 2014, ESOL sold 3,182,253 ordinary shares of Prothena at a price to the public of $26.00 per ordinary share, before the underwriting discount. As a result, ESOL and Perrigo no longer owned any ordinary shares of Prothena as of such sale.
	The Company did not receive any of the proceeds from the offering, and the total number of the Company's ordinary shares outstanding did not change as a result of this offering. The Company paid the expenses associated with the sale of these ordinary shares (other than the underwriting discount, fees and disbursements of counsel for the selling shareholder) pursuant to a Subscription and Registration Rights Agreement dated November 8, 2012 by and between the Company, Elan and ESOL.
	Agreements with Elan
	As described elsewhere in these Condensed Consolidated Financial Statements, the results of operations of the Prothena business for the time period prior to the separation include transactions with Elan. The related party revenue recognized by the Company for the three and nine months ended September 30, 2014 and 2013 consisted of fees arising from R&D services provided to Elan. Additionally, the results of operations for the time period prior to the separation include certain costs allocated from Elan to the Company for centralized support services.
	The Company entered into certain agreements with Elan, including the Transitional Services Agreement and the R&D Services Agreement.
	Transitional Services Agreement
	In December 2012, as amended in March 2013, the Company entered into a Transitional Services Agreement (“TSA”) with Elan under which Elan would provide to the Company, and the Company would 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 included chemistry, manufacturing and controls/quality assurance, information technology services, facilities services, company secretarial services, finance services, legal services, compliance services and human resources services.
	The payment terms of the agreement generally provided that the Company would 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%. Similarly, Elan would pay the Company for the time spent by each of the Company’s employee providing services to Elan, which would 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.
	TSA expenses recognized during the three and nine months ended September 30, 2013 were $nil and $0.5 million (of which $0.1 million was included in R&D expenses and $0.4 million was included in G&A expenses), respectively. The TSA expired on December 31, 2013.
	R&D Services Agreement
	In December 2012, as amended in March 2013, 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 has a term of 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 an uncured 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 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 are substantially similar to research services performed by the Company for Elan prior to the separation and distribution.
	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. There is also a fixed monthly charge of $7,500 to account for lab space and capital equipment used by Elan, for so long as Elan uses such lab space and capital equipment. Revenue recognized by the Company included fees arising from R&D services provided to Elan of $137,000 and $171,000, respectively, for the three months ended September 30, 2014 and 2013, and $412,000 and $509,000 for the nine months ended September 30, 2014 and 2013, respectively.
	Consulting Services Agreement
	In April 2014, the Company entered into an agreement with a non-employee member of its Board of Directors to provide consulting services to the Company in connection with its Parkinson disease (PRX002) drug development program. The Company paid that Board member $nil and $20,000 in the three and nine months ended September 30, 2014, respectively.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Basis of Preparation and Presentation of Financial Information	'
	Basis of Preparation and Presentation of Financial Information
	The accompanying interim Condensed Consolidated Financial Statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (“GAAP”) and with the instructions for Form 10-Q and Regulation S-X. Accordingly, they do not include all of the information and notes required for complete financial statements. These interim Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes thereto contained in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (“SEC”) on March 7, 2014 (the "2013 Form 10-K"). The Condensed Consolidated Financial Statements of Prothena Corporation plc are presented in U.S. dollars, which is the functional currency of the Company. The unaudited condensed consolidated financial statements include the accounts of the Company and its consolidated subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
	Unaudited Interim Financial Information
	The accompanying interim Condensed Consolidated Financial Statements and related disclosures are unaudited, have been prepared on the same basis as the annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for a fair presentation of the results of operations for the periods presented. The year-end condensed balance sheet data was derived from audited financial statements, but does not include all disclosures required by GAAP. The condensed consolidated results of operations for any interim period are not necessarily indicative of the results to be expected for the full year or for any other future year or interim period. Although we achieved net income in the first nine months of 2014, primarily as a result of the $30.0 million upfront payment and the $15.0 million milestone payment under the Roche License Agreement, we expect to incur substantial losses for the foreseeable future.
Use of Estimates	'
	Use of Estimates
	The preparation of the Condensed Consolidated Financial Statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses. Because of the uncertainties inherent in such estimates, actual results may differ materially from these estimates.
Revenue	'
	Revenue Recognition
	Revenue is recognized when earned and non-refundable, when payment is reasonably assured, and when there is no future obligation with respect to the revenue, in accordance with the terms prescribed in the applicable contract.
	Multiple Element Arrangements
	The Company's revenues are generated primarily through its license, development and commercialization agreement. These types of agreements generally contain multiple elements, or deliverables, which may include (i) licenses to the Company's technology, (ii) R&D activities to be performed on behalf of the collaborative partner, and (iii) in certain cases, services or obligations in connection with the manufacturing or supply of pre-clinical and clinical material. Payments to the Company under these arrangements typically include one or more of the following: non-refundable, upfront license fees; funding of research and/or development efforts; milestone payments; and royalties on future product sales.
	Revenue under license, development and commercialization agreements is recognized based on the performance requirements of the contract. Determinations of whether persuasive evidence of an arrangement exists and whether delivery has occurred or services have been rendered are based on management’s judgments regarding the fixed nature of the fees charged for deliverables and the collectability of those fees.
	The Company recognizes revenue related to license, development and commercialization agreements in accordance with the provisions of Financial Accounting Standards Board, or FASB, Accounting Standards Codification, or ASC, Topic 605-25, “Revenue Recognition - Multiple-Element Arrangements.” The Company evaluates all deliverables within an arrangement to determine whether or not they provide value on a stand-alone basis. Based on this evaluation, the deliverables are separated into units of accounting. The arrangement consideration that is fixed or determinable at the inception of the arrangement is allocated to the separate units of accounting based on their relative selling prices.
	To determine the selling price of a separate deliverable, the Company uses the hierarchy as prescribed in ASC Topic 605-25 based on vendor-specific objective evidence (VSOE), third-party evidence (TPE) or best estimate of selling price (BESP). VSOE is based on the price charged when the element is sold separately and is the price actually charged for that deliverable. TPE is determined based on third party evidence for a similar deliverable when sold separately and BESP is the estimated selling price at which we would transact a sale if the elements of collaboration and license arrangements were sold on a stand-alone basis to the buyer.
	Payments or full reimbursements resulting from our R&D efforts for those arrangements where such efforts are considered as deliverables are recognized as the services are performed and are presented on a gross basis so long as there is persuasive evidence of an arrangement, the fee is fixed or determinable, and collection of the related receivable is reasonably assured. However, such funding is recognized as a reduction of R&D expense when the Company engages in a R&D project jointly with another entity, with both entities participating in project activities and sharing costs and potential benefits of the project.
	Milestone Revenue
	The Company accounts for milestones under ASU No. 2010-17, Milestone Method of Revenue Recognition. Under the milestone method, contingent consideration received from the achievement of a substantive milestone is recognized in its entirety in the period in which the milestone is achieved. A milestone is defined as an event (i) that can only be achieved based in whole or in part on either the entity’s performance or on the occurrence of a specific outcome resulting from the entity’s performance, (ii) for which there is substantive uncertainty at the date the arrangement is entered into that the event will be achieved, and (iii) that would result in additional payments being due to the entity. At the inception of an agreement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether (a) the consideration is commensurate with either (1) the entity’s performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the entity’s performance to achieve the milestone, (b) the consideration relates solely to past performance, and (c) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve a particular milestone, the level of effort and investment required to achieve such milestone and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement in making this assessment.
	The Company generally classifies each of its milestones into one of three categories: (i) clinical milestones, (ii) regulatory and development milestones, and (iii) commercial milestones. Clinical milestones are typically achieved when a product candidate advances into or completes a defined phase of clinical research. For example, a milestone payment may be due to the Company upon the initiation of a clinical trial for a new indication. Regulatory and development milestones are typically achieved upon acceptance of the submission for marketing approval of a product candidate or upon approval to market the product candidate by the U.S. Food and Drug Administration (the "FDA") or other regulatory authorities. For example, a milestone payment may be due to the Company upon filing of a Biologics License Application (BLA) with the FDA. Commercial milestones are typically achieved when an approved pharmaceutical product reaches certain defined levels of net royalty sales by the licensee of a specified amount within a specified period.
	Commercial milestone payments and milestone payments that are not deemed to be substantive will be accounted for as a contingent revenue payment with revenue recognized when all contingencies are lifted, which is expected to be upon achievement of the milestone, assuming all revenue recognition criteria are met.
	Profit Share Revenue
	For agreements, with profit sharing arrangements, the Company will record its share of the pre-tax commercial profit as collaboration revenue when the profit sharing can be reasonably estimated and collectability is reasonably assured.
	Royalty Revenue
	The Company will recognize revenue from royalties based on licensees' sales of the Company's products or products using the Company's technologies. Royalties are recognized as earned in accordance with the contract terms when royalties from licensees can be reasonably estimated and collectability is reasonably assured.
Net Income per Ordinary Share	'
	Net Income per Ordinary Share
	Basic net income (loss) per ordinary share is computed by dividing net income (loss) attributable to ordinary shareholders by the weighted average number of ordinary shares outstanding during the period less the weighted average number of unvested restricted ordinary shares subject to the right of repurchase. Diluted net income per ordinary share is computed by giving effect to all dilutive potential ordinary shares including options. However, potentially issuable ordinary shares are not used in computing diluted net loss per ordinary share as their effect would be anti-dilutive due to the loss recorded.
Comprehensive Income (Loss)	'
	Comprehensive Income (Loss)
	Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income (loss). The Company has no components of other comprehensive income (loss). Therefore net income (loss) equals comprehensive income (loss) for all periods presented and, accordingly, the Condensed Consolidated Statements of Comprehensive Income (Loss) is not presented in a separate statement.
Segment and Concentration of Risks	'
	Segment and Concentration of Risks
	The Company operates one segment. The Company’s chief operating decision maker (the “CODM”), its Chief Executive Officer, manages the Company’s operations on a consolidated basis for purposes of allocating resources. When evaluating the Company’s financial performance, the CODM reviews all financial information on a consolidated basis.
	Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents and accounts receivable. The Company places its cash equivalents with high credit quality financial institutions and by policy, limits the amount of credit exposure with any one financial institution. Deposits held with banks may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits of cash and cash equivalents and its credit risk exposure is up to the extent recorded on the Company's consolidated balance sheet.
	All of the Company's long-lived assets were held in the U.S. The Company’s accounts receivable from related party are from Elan located in Ireland for all periods presented. For the three and nine months ended September 30, 2014, receivable from Roche includes amounts due from Roche entities located in the U.S. and Switzerland under the License Agreement that became effective January 22, 2014. Revenue recorded in the Statements of Operations consists of collaboration revenue related to the upfront payment from Roche under the License Agreement, payment from Roche upon achievement of a clinical milestone and reimbursement for research and development services and fees earned from the provision of nonclinical research support to Elan, primarily in the areas of safety, toxicology and regulatory. The fees charged to Elan were calculated based on the expenses incurred by the Company in the provision of those R&D services, plus a contractually determined mark-up of those expenses.
	The Company utilizes Boehringer Ingelheim in Switzerland for its clinical drug product supply for therapeutic antibody programs. An inability to obtain drug product supply on a timely basis could have a material adverse impact on the Company's business, financial condition and results of operations.
Recent Accounting Pronouncements	'
	Emerging Growth Company Status
	As an Emerging Growth Company under the Jumpstart Our Business Startups Act (“JOBS Act”), the Company is eligible to take advantage of certain exemptions from various reporting requirements that apply to other public companies that are not Emerging Growth Companies. The Company has an extended transition period for adopting new or revised accounting standards that have different effective dates for public and private companies until such time as those standards apply to private companies.
	Recent Accounting Pronouncements
	Except for the standards below, there have been no new accounting pronouncements or changes to accounting pronouncements during the nine months ended September 30, 2014, as compared to the recent accounting pronouncements described in our 2013 Form 10-K, that are of significance or potential significance to the Company.
	In May 2014, the FASB issued Accounting Standards Update 2014-09 (ASU 2014-09), Revenue from Contracts with Customers. ASU 2014-09 supersedes the revenue recognition requirements in Revenue Recognition (Topic 605), and requires entities to recognize revenue in a way that depicts the transfer of promised goods and services to customers in an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services. ASU 2014-09 is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period, which for the Company is January 1, 2017. Early adoption is not permitted. The standard permits the use of either retrospective or cumulative effect transition method. The Company is currently evaluating the potential impact the adoption of ASU 2014-09 will have on its consolidated financial statements. The Company has not yet selected a transition method nor has it determined the effect of the standard on its ongoing financial reporting.

Composition_of_Certain_Balance1

Composition of Certain Balance Sheet Items (Tables)	9 Months Ended
	Sep. 30, 2014
Composition of Certain Balance Sheet Items [Abstract]	'
Schedule of Property and Equipment	'
	Property and Equipment, net
	Property and equipment, net consisted of the following (in thousands):
		September 30,			December 31,
		2014			2013
	Machinery and equipment	$	5,789		$	5,649
	Leasehold improvements	2,211			1,927
	Purchased computer software	120			85
		8,120			7,661
	Less: accumulated depreciation and amortization	(4,838		)	(4,289		)
	Property and equipment, net	$	3,282		$	3,372
Schedule of Other Current Liabilities	'
	Other Current Liabilities
	Other current liabilities consisted of the following (in thousands):
		September 30,			December 31,
		2014			2013
	Payroll and related expenses	$	2,315		$	2,800
	Professional services	984			616
	Accrued offering costs	31			82
	Deferred rent	138			138
	Other	346			254
	Other current liabilities	$	3,814		$	3,890

Net_income_loss_Per_Ordinary_S1

Net income (loss) Per Ordinary Share (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Calculation of Basic and Diluted Net Income or Loss Per Share	'
	Net income (loss) per ordinary share was determined as follows (in thousands, except per share amounts):
			Three Months Ended September 30,						Nine Months Ended
									September 30,
			2014			2013			2014		2013
	Numerator (basic and dilutive):
	Net income (loss)		$	(13,182	)	$	(9,689	)	$	5,960	$	(29,942	)
	Denominator (basic):
	Weighted-average ordinary shares outstanding		27,370			17,679			23,758		17,679
	Denominator (diluted):
	Weighted-average ordinary shares outstanding		27,370			17,679			23,758		17,679
	Dilutive stock options outstanding		—			—			964		—
	Net weighted average ordinary shares outstanding		27,370			17,679			24,722		17,679
	Net income (loss) per share attributable to holders of ordinary shares:
	Basic net income (loss) per share		$	(0.48	)	$	(0.55	)	$	0.25	$	(1.69	)
	Diluted net income (loss) per share		$	(0.48	)	$	(0.55	)	$	0.24	$	(1.69	)
Ordinary Shares Equivalent Not Included in Diluted Net Loss Per Share	'
	The equivalent ordinary shares not included in diluted net income (loss) per share because their effect would be anti-dilutive are as follows (in thousands):
		Three Months Ended September 30,					Nine Months Ended
							September 30,
		2014			2013		2014		2013
	Options to purchase ordinary shares	777			57		632		76
	Total	777			57		632		76

Commitment_and_Contingencies_T

Commitment and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Schedule of Operating Lease Commitments	'
	Future minimum payments under operating leases as of September 30, 2014, are as follows (in thousands):
	Year Ended December 31,		Operating Lease
	2014 (Remaining 3 months)		$	368
	2015		1,834
	2016		1,938
	2017		2,017
	2018		2,096
	Thereafter		4,237
	Total future minimum lease payments		$	12,490
Schedule of Contractual Obligations by Fiscal Year Maturity	'
	The following is a summary of the Company's non-cancelable purchase commitments and contractual obligations as of September 30, 2014 (in thousands):
		Total			2014		2015		2016		2017		2018		Thereafter
					(Remaining 3 months)
	Purchase Obligations	$	3,170		$	3,170	$	—	$	—	$	—	$	—	$	—
	Contractual obligations under license agreements (1)	1,225			135		100		100		100		100		690
	Total	$	4,395		$	3,305	$	100	$	100	$	100	$	100	$	690
	(1) Excludes future obligations pursuant to the cost-sharing arrangement under the Company's License Agreement with Roche. Amounts of such obligations, if any, cannot be determined at this time.

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2014
Summary of Share-Based Compensation Expense	'
	The following table summarizes share-based compensation expense for the periods presented (in thousands):
		Three Months Ended September 30,								Nine Months Ended
										September 30,
		2014				2013				2014				2013
	Research and development(1)	$	601			$	311			$	1,650			$	616
	General and administrative	817				644				2,549				1,421
	Total	$	1,418			$	955			$	4,199			$	2,037
	_________________
	(1)	Includes $20,000 and $108,000 for the three months ended September 30, 2014 and 2013, respectively, and $92,000 and $171,000 for the nine months ended September 30, 2014 and 2013, respectively, of share-based compensation expense related to options granted to a consultant.
Amended and Restated 2012 Long Term Incentive Plan	'
Fair Value of Options Granted	'
	The fair value of the options granted to employees and non-employee directors during the three and nine months ended September 30, 2014 and 2013 is estimated as of the grant date using the Black-Scholes option-pricing model assuming the weighted-average assumptions listed in the following table:
			Three Months Ended September 30,				Nine Months Ended
							September 30,
			2014		2013		2014		2013
	Expected volatility		86.30%		81.00%		84.50%		84.10%
	Risk-free interest rate		1.90%		1.80%		1.80%		1.20%
	Expected dividend yield		—%		—%		—%		—%
	Expected life (in years)		6		6		6		6
	Weighted average grant date fair value		$15.01		$12.56		$20.03		$4.97
Summary of Company's Share Option Activity	'
	The following table summarizes the Company’s share option activity during the nine months ended September 30, 2014:
		Options			Weighted				Weighted		Aggregate
					Average				Average		Intrinsic
					Exercise				Remaining		Value
					Price				Contractual		(in thousands)
									Term (years)
	Outstanding at December 31, 2013	1,973,500			$	7.5			9.17		$	37,528
	Granted	710,500			28.1
	Exercised	(62,863	)		7.05
	Canceled	—			—
	Outstanding at September 30, 2014	2,621,137			$	13.1			8.7		$	28,173
	Vested and expected to vest at September 30, 2014	2,528,276			$	12.95			8.69		$	27,461
	Vested at September 30, 2014	900,323			$	7.23			8.41		$	13,442
Summary of Options Outstanding and Exercisable by Exercise Price	'
	The following table summarizes information about the Company's share options outstanding as of September 30, 2014:
								Options Outstanding								Options Exercisable
	Range of Exercise Prices							Number of Options			Weighted -		Weighted Average Exercise Price			Number of Options	Weighted Average Exercise Price
											Average
											Remaining
											Contractual Life
											(Years)
	$	6.03		$	6.03			453,375			8.33		$	6.03		188,250	$	6.03
	6.41			6.41				808,762			8.33		6.41			428,845	6.41
	6.65			6.65				50,000			8.46		6.65			50,000	6.65
	6.73			6.73				366,000			8.5		6.73			148,541	6.73
	8.21			22.14				346,500			9.14		17.26			84,687	15.26
	23.11			23.11				27,500			9.92		23.11			—	—
	24.26			24.26				30,000			9.09		24.26			—	—
	29.52			29.52				25,000			9.34		29.52			—	—
	29.81			29.81				484,000			9.35		29.81			—	—
	37.02			37.02				30,000			9.5		37.02			—	—
	$	6.03		$	37.02			2,621,137			8.7		$	13.1		900,323	$	7.23

Organization_Additional_Inform

Organization - Additional Information (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Feb. 28, 2014	31-May-14	Jul. 31, 2014
					License	Collaborative Arrangement	Underwritten Public And Over-Allotment Offering
					Roche	Roche	Ordinary Shares
Organization [Line Items]	'	'	'	'	'	'	'
Accumulated deficit	$35,381,000	$41,341,000	'	'	'	'	'
Cash and cash equivalents	306,153,000	176,677,000	101,859,000	124,860,000	'	'	'
Upfront payment pursuant to License Agreement	'	'	'	'	30,000,000	'	'
Clinical milestone received	'	'	'	'	'	15,000,000	'
Shares sold pursuant to underwritten public offering (in shares)	'	'	'	'	'	'	5,462,500
Net proceeds from issuance of ordinary shares in underwritten public offering	'	'	'	'	'	'	$117,400,000

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Details) (Roche, USD $)	1 Months Ended
In Millions, unless otherwise specified	Feb. 28, 2014	31-May-14
	License	Collaborative Arrangement
Accounting Policies [Line Items]	'	'
Upfront payment pursuant to License Agreement	$30	'
Clinical milestone received	'	$15

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (Level 1, USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Level 1	'	'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'	'
Money Market Funds at Carrying Value	$275.10	$153.30

Composition_of_Certain_Balance2

Composition of Certain Balance Sheet Items - Schedule of Property and Equipment (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Composition of Certain Balance Sheet Items [Abstract]	'	'
Machinery and equipment	$5,789	$5,649
Leasehold improvements	2,211	1,927
Purchased computer software	120	85
Property and equipment, gross	8,120	7,661
Less: accumulated depreciation and amortization	-4,838	-4,289
Property and equipment, net	$3,282	$3,372

Composition_of_Certain_Balance3

Composition of Certain Balance Sheet Items - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Composition of Certain Balance Sheet Items [Abstract]	'	'	'	'
Depreciation and amortization	$200	$100	$549	$428

Composition_of_Certain_Balance4

Composition of Certain Balance Sheet Items - Schedule of Other Current Liabilities (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Composition of Certain Balance Sheet Items [Abstract]	'	'
Payroll and related expenses	$2,315	$2,800
Professional services	984	616
Accrued offering costs	31	82
Deferred rent	138	138
Other	346	254
Other current liabilities	$3,814	$3,890

Net_income_loss_Per_Ordinary_S2

Net income (loss) Per Ordinary Share - Calculation of Basic and Diluted Net Income or Loss Per Share (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:	'	'	'	'
Net income (loss)	($13,182)	($9,689)	$5,960	($29,942)
Denominator	'	'	'	'
Weighted-average ordinary shares outstanding (in shares)	27,370	17,679	23,758	17,679
Dilutive stock options outstanding (in shares)	0	0	964	0
Net weighted average ordinary shares outstanding (in shares)	27,370	17,679	24,722	17,679
Net income (loss) per share attributable to holders of ordinary shares	'	'	'	'
Basic (in dollars per share)	($0.48)	($0.55)	$0.25	($1.69)
Diluted (in dollars per share)	($0.48)	($0.55)	$0.24	($1.69)

Net_income_loss_Per_Ordinary_S3

Net income (loss) Per Ordinary Share - Ordinary Shares Equivalent Not Included in Diluted Net Loss Per Share (Detail)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Equivalent ordinary shares not included in diluted net loss per share	777	57	632	76
Options to purchase ordinary shares	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Equivalent ordinary shares not included in diluted net loss per share	777	57	632	76

Commitment_and_Contingencies_L

Commitment and Contingencies - Lease Narrative (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Long-term Purchase Commitment [Line Items]	'	'	'	'
Rent expense	$0.50	$0.30	$1.30	$0.90
Noncancelable operating lease agreement	'	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'	'
Expiration of lease	'	'	30-Nov-20	'
Rent expense	'	'	$1.90	'
Area of rentable square feet	50,400	'	50,400	'

Commitment_and_Contingencies_C

Commitment and Contingencies - Commitment Narrative (Details) (USD $)	Sep. 30, 2014
Long-term Purchase Commitment [Line Items]	'
Purchase Obligation	$3,170,000
Contractual Obligations Under License Agreements	1,225,000	[1]
Accrued current liabilities	'
Long-term Purchase Commitment [Line Items]	'
Commitment to suppliers included in accrued current liabilities	3,000,000
Contractual Obligations under License Agreements included in accrued current liabilities	100,000
License agreements	'
Long-term Purchase Commitment [Line Items]	'
Contractual Obligations Under License Agreements	$1,225,000
[1]	Excludes future obligations pursuant to the cost-sharing arrangement under the Company's License Agreement with Roche. Amounts of such obligations, if any, cannot be determined at this time.

Commitment_and_Contingencies_C1

Commitment and Contingencies Commitment and Contingencies - Schedule of Operating Lease Commitment (Details) (USD $)	Sep. 30, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]	'
2014 (Remaining 3 Months)	$368
2015	1,834
2016	1,938
2017	2,017
2018	2,096
Thereafter	4,237
Total future minimum lease payments	$12,490

Commitment_and_Contingencies_C2

Commitment and Contingencies Commitment and Contingencies - Contractual Obligations (Details) (USD $)	Sep. 30, 2014
In Thousands, unless otherwise specified
Purchase Obligation, Fiscal Year Maturity [Abstract]	'
Total	$3,170
2014 (Remaining 3 Months)	3,170
2015	0
2016	0
2017	0
2018	0
Thereafter	0
Contractual Obligation, Fiscal Year Maturity [Abstract]	'
Total	1,225	[1]
2014 (Remaining 3 Months)	135	[1]
2015	100	[1]
2016	100	[1]
2017	100	[1]
2018	100	[1]
Thereafter	690	[1]
Purchase and Contractual Obligations, Fiscal Year Maturity [Abstract]	'
Total	4,395
2014 (Remaining 3 Months)	3,305
2015	100
2016	100
2017	100
2018	100
Thereafter	$690
[1]	Excludes future obligations pursuant to the cost-sharing arrangement under the Company's License Agreement with Roche. Amounts of such obligations, if any, cannot be determined at this time.

Significant_Agreements_Details

Significant Agreements (Details) (USD $)

9 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

3 Months Ended

Sep. 30, 2014

31-May-14

Sep. 30, 2014

Jun. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Feb. 28, 2014

Sep. 30, 2014

Sep. 30, 2014

Collaborative Arrangement

Collaborative Arrangement

Collaborative Arrangement

Collaborative Arrangement

Collaborative Arrangement

Research Reimbursement

Research Reimbursement

Development Costs Reimbursement

Development Costs Reimbursement

License

Scenario, Previously Reported [Member]

Scenario, Adjustment [Member]

Roche

Roche

Roche

Roche

Roche

Roche

Roche

Roche

Roche

Collaborative Arrangement

Collaborative Arrangement

Roche

Roche

License Agreement [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Upfront payment pursuant to License Agreement

'

'

'

'

'

'

'

'

'

$30,000,000

'

'

Clinical milestone received

'

15,000,000

'

'

'

'

'

'

'

'

'

'

Collaboration service revenue recognized for research services

'

'

'

'

'

400,000

1,100,000

'

'

'

'

'

Cost Sharing payments made recognized as R&D expenses

'

'

500,000

'

1,000,000

'

'

'

'

'

'

'

Potential payment upon achievement of development, regulatory and various first commercial sales milestones

'

'

'

'

380,000,000

'

'

'

'

'

'

'

Potential payment for achievement of non U.S.commercial sales milestones

'

'

'

'

175,000,000

'

'

'

'

'

'

'

Potential alternative commercial sales milestone payment

'

'

'

'

155,000,000

'

'

'

'

'

'

'

Portion of revenue and expenses attributable to company, percentage

30.00%

'

'

'

70.00%

'

'

'

'

'

'

'

Multiple element consideration, relative sales price method, amount allocable to license

'

'

'

'

'

'

'

'

'

'

34,700,000

35,600,000

Development reimbursement

'

'

1,000,000

'

4,500,000

'

'

'

'

'

'

'

Development reimbursement recognized as collaboration license revenue

'

'

'

'

'

'

'

900,000

4,000,000

'

'

'

Development Reimbursement Recognized As Offset To Research And Development Expense

'

'

'

'

'

'

'

100,000

500,000

'

'

'

Milestone payment recognized as collaboration revenue

'

'

'

13,300,000

'

'

'

'

'

'

'

'

Milestone payment used as offset to R&D expense

'

'

'

$1,700,000

'

'

'

'

'

'

'

'

Shareholders_Equity_Ordinary_S

Shareholder's Equity (Ordinary Shares/Euro Deferred Shares) (Details)

9 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

2 Months Ended

1 Months Ended

In Millions, except Share data, unless otherwise specified

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Dec. 31, 2013

Feb. 28, 2014

Jun. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Jul. 31, 2014

Jun. 30, 2014

Jun. 30, 2014

Jul. 31, 2014

USD ($)

EUR (€)

USD ($)

EUR (€)

Ordinary Shares

Underwritten Public Offering [Member]

Underwritten Public Offering [Member]

Underwritten Public Offering [Member]

Underwritten Public And Over-Allotment Offering

Underwritten Public Offering [Member]

Underwritten Public Offering [Member]

Underwritten Public Offering [Member]

vote

vote

Perrigo

USD ($)

USD ($)

USD ($)

Ordinary Shares

USD ($)

Ordinary Shares

Over-Allotment Option [Member]

USD ($)

USD ($)

USD ($)

Shareholders Equity [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Ordinary shares, number of authorized shares

100,000,000

100,000,000

100,000,000

100,000,000

'

'

'

'

'

'

'

'

Ordinary shares, par value (in dollars per share)

$0.01

'

$0.01

'

'

'

'

'

'

'

'

'

Ordinary shares, number of issued shares

27,381,624

27,381,624

21,856,261

21,856,261

'

'

'

'

'

'

'

'

Ordinary shares, number of outstanding shares

27,381,624

27,381,624

21,856,261

21,856,261

'

'

'

'

'

'

'

'

Votes per share

1

1

'

'

'

'

'

'

'

'

'

'

Euro deferred shares, number of shares authorized

10,000

10,000

10,000

10,000

'

'

'

'

'

'

'

'

Euro deferred shares, nominal value (in euros per share)

'

€ 22

'

€ 22

'

'

'

'

'

'

'

'

Euro deferred shares, number of outstanding shares

0

0

0

0

'

'

'

'

'

'

'

'

Shares sold pursuant to underwritten public offering

'

'

'

'

3,182,253

'

'

'

'

'

'

'

Share price (in dollars per share)

'

'

'

'

$26

'

'

'

'

'

'

'

Shares sold pursuant to underwritten public offering (in shares)

'

'

'

'

'

'

'

'

5,462,500

'

4,750,000

712,500

Share price (in dollars per share)

'

'

'

'

'

'

'

'

'

$22.50

'

'

Net proceeds received for the sale of shares

'

'

'

'

'

$102.50

'

'

'

'

'

'

Public offering costs

'

'

'

'

'

'

-1.2

-5.5

'

'

'

'

Net proceeds from issuance of ordinary shares in underwritten public offering

'

'

'

'

'

'

'

'

117.4

'

'

14.9

Underwriting Discounts

'

'

'

'

'

'

'

'

'

'

'

($1.10)

ShareBased_Compensation_Summar

Share-Based Compensation - Summary of Share-Based Compensation Expense (Detail) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'		'		'
Share-based compensation expense	$1,418		$955		$4,199		$2,037
Research and development	'		'		'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'		'		'
Share-based compensation expense	601	[1]	311	[1]	1,650	[1]	616	[1]
General and administrative	'		'		'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'		'		'
Share-based compensation expense	$817		$644		$2,549		$1,421
[1]	Includes $20,000 and $108,000 for the three months ended September 30, 2014 and 2013, respectively, and $92,000 and $171,000 for the nine months ended September 30, 2014 and 2013, respectively, of share-based compensation expense related to options granted to a consultant

ShareBased_Compensation_Fair_V

Share-Based Compensation - Fair Value of Options Granted (Detail) (Amended and Restated 2012 Long Term Incentive Plan, USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Amended and Restated 2012 Long Term Incentive Plan	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Expected volatility	86.30%	81.00%	84.47%	84.10%
Risk-free interest rate	1.91%	1.80%	1.82%	1.20%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected life	'6 years	'6 years	'6 years	'6 years
Weighted average fair value	$15.01	$12.56	$20.03	$4.97

Sharebased_Compensation_Shareb

Share-based Compensation - Share-based Compensation Plan - Option Activity (Detail) (Amended and Restated 2012 Long Term Incentive Plan, USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Amended and Restated 2012 Long Term Incentive Plan	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'	'	'	'	'
Options, Outstanding beginning balance	'	'	1,973,500	'	'
Options, granted	47,500	99,000	710,500	1,934,500	'
Options, exercised	'	'	-62,863	'	'
Options, canceled	'	'	0	'	'
Options, Outstanding ending balance	2,621,137	'	2,621,137	'	1,973,500
Options, Vested and expected to vest ending balance	2,528,276	'	2,528,276	'	'
Options vested	900,323	'	900,323	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]	'	'	'	'	'
Weighted Average Exercise Price, Outstanding beginning balance	'	'	$7.50	'	'
Weighted Average Exercise Price, Granted	'	'	$28.10	'	'
Weighted Average Exercise Price, Exercised	'	'	$7.05	'	'
Weighted Average Exercise Price, Canceled	'	'	$0	'	'
Weighted Average Exercise Price, Outstanding ending balance	$13.10	'	$13.10	'	$7.50
Weighted Average Exercise Price, Vested and expected to vest ending balance	$12.95	'	$12.95	'	'
Weighted Average Exercise Price, Vested	$7.23	'	$7.23	'	'
Weighted Average Remaining Contractual Life (Years), Outstanding	'	'	'8 years 8 months 12 days	'	'9 years 2 months 1 day
Weighted Average Remaining Contractual Life (Years), Vested and expected to vest ending balance	'	'	'8 years 8 months 9 days	'	'
Aggregate Intrinsic Value, Outstanding beginning balance	'	'	$37,528	'	'
Aggregate Intrinsic Value, Outstanding ending balance	28,173	'	28,173	'	37,528
Aggregate Intrinsic Value, Vested and expected to vest ending balance	27,461	'	27,461	'	'
Aggregate Intrinsic Value, Vested	$13,442	'	$13,442	'	'
Weighted Average Remaining Contractual Life (Years), Vested	'	'	'8 years 4 months 28 days	'	'

ShareBased_Compensation_Exerci

Share-Based Compensation - Exercise Price (Details) (Amended and Restated 2012 Long Term Incentive Plan, USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$6.03	'
Exercise price, upper limit (in dollars per share)	$37.02	'
Number of options outstanding	2,621,137	'
Options outstanding, weighted-average remaining contractual life	'8 years 8 months 12 days	'9 years 2 months 1 day
Options outstanding, weighted average exercise price (in dollars per share)	$13.10	'
Number of shares exercisable	900,323	'
Options exercisable, weighted average exercise price (in dollars per share)	$7.23	'
$6.03 - $6.03	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$6.03	'
Exercise price, upper limit (in dollars per share)	$6.03	'
Number of options outstanding	453,375	'
Options outstanding, weighted-average remaining contractual life	'8 years 3 months 29 days	'
Options outstanding, weighted average exercise price (in dollars per share)	$6.03	'
Number of shares exercisable	188,250	'
Options exercisable, weighted average exercise price (in dollars per share)	$6.03	'
$6.41 - $6.41	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$6.41	'
Exercise price, upper limit (in dollars per share)	$6.41	'
Number of options outstanding	808,762	'
Options outstanding, weighted-average remaining contractual life	'8 years 3 months 29 days	'
Options outstanding, weighted average exercise price (in dollars per share)	$6.41	'
Number of shares exercisable	428,845	'
Options exercisable, weighted average exercise price (in dollars per share)	$6.41	'
$6.65 - $6.65	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$6.65	'
Exercise price, upper limit (in dollars per share)	$6.65	'
Number of options outstanding	50,000	'
Options outstanding, weighted-average remaining contractual life	'8 years 5 months 16 days	'
Options outstanding, weighted average exercise price (in dollars per share)	$6.65	'
Number of shares exercisable	50,000	'
Options exercisable, weighted average exercise price (in dollars per share)	$6.65	'
$6.73 - $6.73	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$6.73	'
Exercise price, upper limit (in dollars per share)	$6.73	'
Number of options outstanding	366,000	'
Options outstanding, weighted-average remaining contractual life	'8 years 6 months	'
Options outstanding, weighted average exercise price (in dollars per share)	$6.73	'
Number of shares exercisable	148,541	'
Options exercisable, weighted average exercise price (in dollars per share)	$6.73	'
$8.21 - $22.14	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$8.21	'
Exercise price, upper limit (in dollars per share)	$22.14	'
Number of options outstanding	346,500	'
Options outstanding, weighted-average remaining contractual life	'9 years 1 month 21 days	'
Options outstanding, weighted average exercise price (in dollars per share)	$17.26	'
Number of shares exercisable	84,687	'
Options exercisable, weighted average exercise price (in dollars per share)	$15.26	'
$23.11 - $23.11	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$23.11	'
Exercise price, upper limit (in dollars per share)	$23.11	'
Number of options outstanding	27,500	'
Options outstanding, weighted-average remaining contractual life	'9 years 11 months 1 day	'
Options outstanding, weighted average exercise price (in dollars per share)	$23.11	'
Number of shares exercisable	0	'
Options exercisable, weighted average exercise price (in dollars per share)	$0	'
$24.26 - $24.26	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$24.26	'
Exercise price, upper limit (in dollars per share)	$24.26	'
Number of options outstanding	30,000	'
Options outstanding, weighted-average remaining contractual life	'9 years 1 month 2 days	'
Options outstanding, weighted average exercise price (in dollars per share)	$24.26	'
Number of shares exercisable	0	'
Options exercisable, weighted average exercise price (in dollars per share)	$0	'
$29.52 - $29.52	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$29.52	'
Exercise price, upper limit (in dollars per share)	$29.52	'
Number of options outstanding	25,000	'
Options outstanding, weighted-average remaining contractual life	'9 years 4 months 2 days	'
Options outstanding, weighted average exercise price (in dollars per share)	$29.52	'
Number of shares exercisable	0	'
Options exercisable, weighted average exercise price (in dollars per share)	$0	'
$29.81 - $29.81	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$29.81	'
Exercise price, upper limit (in dollars per share)	$29.81	'
Number of options outstanding	484,000	'
Options outstanding, weighted-average remaining contractual life	'9 years 4 months 6 days	'
Options outstanding, weighted average exercise price (in dollars per share)	$29.81	'
Number of shares exercisable	0	'
Options exercisable, weighted average exercise price (in dollars per share)	$0	'
$37.02 - $37.02	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Exercise price, lower limit (in dollars per share)	$37.02	'
Exercise price, upper limit (in dollars per share)	$37.02	'
Number of options outstanding	30,000	'
Options outstanding, weighted-average remaining contractual life	'9 years 6 months	'
Options outstanding, weighted average exercise price (in dollars per share)	$37.02	'
Number of shares exercisable	0	'
Options exercisable, weighted average exercise price (in dollars per share)	$0	'

ShareBased_Compensation_Additi

Share-Based Compensation - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended
	31-May-14	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Amended and Restated 2012 Long Term Incentive Plan	'	'	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'	'	'
Grant period	'	'	'	'10 years	'	'
Authorized shares for issuance	'	5,550,000	'	5,550,000	'	'
Number of stock options granted to employees	'	47,500	99,000	710,500	1,934,500	'
Vesting period	'	'	'	'4 years	'	'
Number of shares available for grant	'	2,866,000	'	2,866,000	'	'
Options outstanding	'	2,621,137	'	2,621,137	'	1,973,500
Weighted average exercise price	'	$13.10	'	$13.10	'	$7.50
Additional shares authorized	2,900,000	'	'	'	'	'
Unearned share-based compensation estimated to be expense through 2017	'	$17,400,000	'	$17,400,000	'	'
Recognition period of unearned share-based compensation	'	'	'	'2 years 9 months 18 days	'	'
Consultant [Member]	'	'	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'	'	'
Share based compensation expense, non employee	'	$20,000	108,000	$92,000	171,000	'

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'	'	'	'
Provision for income taxes	$241	$137	$688	$267
Ireland statutory income tax rate	'	'	12.50%	12.50%

Related_Parties_Additional_Inf

Related Parties - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

0 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 20, 2012

Dec. 31, 2012

Feb. 28, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2013

Transitional Services Agreement [Member]

Transitional Services Agreement [Member]

Transitional Services Agreement [Member]

R&D Services Agreement [Member]

R&D Services Agreement [Member]

R&D Services Agreement [Member]

R&D Services Agreement [Member]

R&D Services Agreement [Member]

Elan

Elan

Ordinary Shares

Director [Member]

Director [Member]

Research and Development Expense [Member]

General and Administrative Expense [Member]

Transitional Services Agreement [Member]

Perrigo

Consulting [Member]

Consulting [Member]

Transitional Services Agreement [Member]

Transitional Services Agreement [Member]

Related Party Transaction [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of voting interests acquired

'

'

'

'

'

'

'

'

'

'

'

'

18.00%

'

'

'

'

'

'

Issuance of ordinary shares to Elan, shares

'

'

'

'

'

'

'

'

'

'

'

'

3,182,253

'

'

'

'

'

'

Shares sold pursuant to underwritten public offering

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3,182,253

'

'

'

'

Share price (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$26

'

'

'

'

Additional percentage of employee service payment

'

'

'

'

40.00%

'

'

'

'

'

'

'

'

40.00%

'

'

'

'

'

Related Party Transaction, Expenses from Transactions with Related Party

'

'

'

'

'

$0

$500,000

'

'

'

'

'

'

'

'

'

'

$100,000

$400,000

Research and development service agreement (in years)

'

'

'

'

'

'

'

'2 years

'

'

'

'

'

'

'

'

'

'

'

Fixed service fee, annual rate

'

'

'

'

'

'

'

500,000

'

'

'

'

'

'

'

'

'

'

'

Fixed service fee per employee, annual rate

'

'

'

'

'

'

'

250,000

'

'

'

'

'

'

'

'

'

'

'

Variable service fee, annual rate

'

'

'

'

'

'

'

250,000

'

'

'

'

'

'

'

'

'

'

'

Percentage of mark-up applied to fixed and variable charge

'

'

'

'

'

'

'

10.00%

'

'

'

'

'

'

'

'

'

'

'

Fixed monthly charge for lab space and capital equipment used

'

'

'

'

'

'

'

7,500

'

'

'

'

'

'

'

'

'

'

'

Revenues

137,000

171,000

412,000

509,000

'

'

'

'

137,000

171,000

412,000

509,000

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'

'

'

'

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Amount paid to related party

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'

'

'

'

'

'

'

'

'

'

'

'

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'

$0

$20,000

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'