Related Party Transactions	12 Months Ended
Mar. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions (A) Services Agreements: In July 2016, the Company entered into a formal services agreement with RSI (the “Services Agreement”) effective April 29, 2016, under which RSI agreed to provide certain administrative and research and development services to the Company. Under the Services Agreement, the Company pays or reimburses RSI for any expenses it, or third parties acting on its behalf, incurs for the Company. For any general and administrative and research and development activities performed by RSI employees, RSI charges back the employee compensation expense plus a pre-determined mark-up. RSI also provided such services prior to the formalization of the Services Agreement, and such costs have been recognized by the Company in the period in which the services were rendered. Employee compensation expense, inclusive of base salary and fringe benefits, is determined based upon the relative percentage of time utilized on Company matters, which the Company believes is reasonable. All other costs are billed back at cost. The accompanying consolidated financial statements include third-party expenses that have been paid by RSI and RSL. During the year ended March 31, 2017, RSL and RSI provided certain administrative services on behalf of the Company during the formative period of the Company. Total compensation expense, inclusive of base salary, fringe benefits and share-based compensation, is proportionately allocated to the Company based upon the relative percentage of time utilized on the Company’s matters. Under the Services Agreement, for the year ended March 31, 2017 and the period from February 2, 2016 (Date of Inception) to March 31, 2016, the Company incurred expenses of $9.2 million and $0.4 million, respectively, inclusive of the mark-up. In February 2017, in connection with the contribution and assignment of all of the Company's intellectual property rights to MSG, the Company and MSI amended and restated the Services Agreement, effective as of November 11, 2016, to include MSG as a recipient of from MSI. In addition, in February 2017, MSG entered into a separate services agreement with RSG, a wholly-owned subsidiary of RSL, effective as of November 11, 2016, for the provisioning of services by RSG to MSG in relation to the identification of potential product candidates and project management of clinical trials, as well as other services related to clinical development, administrative and financial activities. Under the terms of both services agreements, the Company is obligated to pay or reimburse RSI and RSG for the costs they, or third parties acting on their behalf, incur in providing services to us, including administrative and support services, as well as research and development services. In addition, the Company is obligated to pay to RSI and RSG a pre-determined mark-up on the costs incurred directly by RSI and RSG in connection with any general and administrative and research and development services. (B) Option Agreement: In June 2016, the Company entered into an option agreement with RSL pursuant to which RSL granted to the Company an option to acquire the rights to products to which RSL or any nonpublic affiliate of RSL acquires the rights (other than a relugolix product or a competing product) for uterine fibroids or endometriosis, or for which the primary target indication is advanced prostate cancer. The Company’s option is exercisable at any time during the period commencing upon the completion of its IPO and ending two years following the date of first commercial sale of a relugolix product in a major market country. If the Company elects to exercise its option for a product, it will be required to reimburse RSL for 110% of any payments made by RSL or its affiliate for such product, and will receive an assignment of the agreement through which RSL or its affiliate acquired the rights to such product. (C) Information Sharing and Cooperation Agreement: In July 2016, the Company entered into an information sharing and cooperation agreement, or the Cooperation Agreement, with RSL. The Cooperation Agreement, among other things: (1) obligates the Company to deliver periodic financial statements and other financial information to RSL and to comply with other specified financial reporting requirements; and (2) requires the Company to supply certain material information to RSL to assist it in preparing any future SEC filings. Subject to specified exceptions, the Cooperation Agreement will terminate upon the earlier of the mutual written consent of the parties or when RSL is no longer required by U.S. GAAP to consolidate the Company’s results of operations and financial position, account for its investment in the Company under the equity method of accounting or, by any rule of the SEC, include the Company’s separate financial statements in any filings it may make with the SEC. (D) Manufacture and Supply Agreement: In June 2016, the Company and Takeda’s affiliate, Takeda Pharmaceutical Company Limited, or Takeda Limited, entered into an agreement for the manufacture and supply of relugolix. Under this agreement, Takeda Limited will supply the Company, and the Company will obtain from Takeda Limited, all of its requirements for relugolix drug substance and drug product to be used under its development plans for all indications. If the Company requests, Takeda Limited will assist it with a technical transfer of the manufacturing process for relugolix to it or its designee and the Company will pay the expenses related to such transfer.

Related Party Transactions

(A) Services Agreements:

In July 2016, the Company entered into a formal services agreement with RSI (the “Services Agreement”) effective April 29, 2016, under which RSI agreed to provide certain administrative and research and development services to the Company. Under the Services Agreement, the Company pays or reimburses RSI for any expenses it, or third parties acting on its behalf, incurs for the Company. For any general and administrative and research and development activities performed by RSI employees, RSI charges back the employee compensation expense plus a pre-determined mark-up. RSI also provided such services prior to the formalization of the Services Agreement, and such costs have been recognized by the Company in the period in which the services were rendered. Employee compensation expense, inclusive of base salary and fringe benefits, is determined based upon the relative percentage of time utilized on Company matters, which the Company believes is reasonable. All other costs are billed back at cost. The accompanying consolidated financial statements include third-party expenses that have been paid by RSI and RSL.

During the year ended March 31, 2017, RSL and RSI provided certain administrative services on behalf of the Company during the formative period of the Company. Total compensation expense, inclusive of base salary, fringe benefits and share-based compensation, is proportionately allocated to the Company based upon the relative percentage of time utilized on the Company’s matters. Under the Services Agreement, for the year ended March 31, 2017 and the period from February 2, 2016 (Date of Inception) to March 31, 2016, the Company incurred expenses of $9.2 million and $0.4 million, respectively, inclusive of the mark-up.

In February 2017, in connection with the contribution and assignment of all of the Company's intellectual property rights to MSG, the Company and MSI amended and restated the Services Agreement, effective as of November 11, 2016, to include MSG as a recipient of from MSI. In addition, in February 2017, MSG entered into a separate services agreement with RSG, a wholly-owned subsidiary of RSL, effective as of November 11, 2016, for the provisioning of services by RSG to MSG in relation to the identification of potential product candidates and project management of clinical trials, as well as other services related to clinical development, administrative and financial activities. Under the terms of both services agreements, the Company is obligated to pay or reimburse RSI and RSG for the costs they, or third parties acting on their behalf, incur in providing services to us, including administrative and support services, as well as research and development services. In addition, the Company is obligated to pay to RSI and RSG a pre-determined mark-up on the costs incurred directly by RSI and RSG in connection with any general and administrative and research and development services.

(B) Option Agreement:

In June 2016, the Company entered into an option agreement with RSL pursuant to which RSL granted to the Company an option to acquire the rights to products to which RSL or any nonpublic affiliate of RSL acquires the rights (other than a relugolix product or a competing product) for uterine fibroids or endometriosis, or for which the primary target indication is advanced prostate cancer. The Company’s option is exercisable at any time during the period commencing upon the completion of its IPO and ending two years following the date of first commercial sale of a relugolix product in a major market country. If the Company elects to exercise its option for a product, it will be required to reimburse RSL for 110% of any payments made by RSL or its affiliate for such product, and will receive an assignment of the agreement through which RSL or its affiliate acquired the rights to such product.

In July 2016, the Company entered into an information sharing and cooperation agreement, or the Cooperation Agreement, with RSL. The Cooperation Agreement, among other things: (1) obligates the Company to deliver periodic financial statements and other financial information to RSL and to comply with other specified financial reporting requirements; and (2) requires the Company to supply certain material information to RSL to assist it in preparing any future SEC filings. Subject to specified exceptions, the Cooperation Agreement will terminate upon the earlier of the mutual written consent of the parties or when RSL is no longer required by U.S. GAAP to consolidate the Company’s results of operations and financial position, account for its investment in the Company under the equity method of accounting or, by any rule of the SEC, include the Company’s separate financial statements in any filings it may make with the SEC.

(D) Manufacture and Supply Agreement:

In June 2016, the Company and Takeda’s affiliate, Takeda Pharmaceutical Company Limited, or Takeda Limited, entered into an agreement for the manufacture and supply of relugolix. Under this agreement, Takeda Limited will supply the Company, and the Company will obtain from Takeda Limited, all of its requirements for relugolix drug substance and drug product to be used under its development plans for all indications. If the Company requests, Takeda Limited will assist it with a technical transfer of the manufacturing process for relugolix to it or its designee and the Company will pay the expenses related to such transfer.