Subsequent Events	12 Months Ended
Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events (A) Private Placement with RSL On April 2, 2018, the Company entered into a share purchase agreement, or the Purchase Agreement, with RSL pursuant to which the Company agreed to issue and sell to RSL 1,110,015 of its common shares at a purchase price of $20.27 per common share in a private placement, or the Private Placement. In April 2018, the Company received gross proceeds of $22.5 million from RSL at the closing of the Private Placement. (B) At-the-Market Equity Offering Program On April 2, 2018, the Company entered into a sales agreement, or the Sales Agreement, with Cowen and Company, LLC, or Cowen, to sell its common shares having an aggregate offering price of up to $100.0 million from time to time through an “at-the-market” equity offering program under which Cowen acts as the Company’s agent. In the first quarter of fiscal year 2018, the Company issued and sold 2,767,129 of its common shares under the Sales Agreement. The common shares were sold at a weighted-average-price of $21.47 per common share for aggregate net proceeds to the Company of approximately $57.6 million, after deducting commissions. (C) Commercial Manufacturing and Supply Agreement with Takeda In May 2018, the Company entered into a Commercial Manufacturing and Supply Agreement with Takeda, or the Takeda Commercial Supply Agreement. Pursuant to the Takeda Commercial Supply Agreement, Takeda has agreed to supply the Company and the Company has agreed to obtain from Takeda certain quantities of relugolix drug substance according to agreed-upon quality specifications and in order to commercialize relugolix in accordance with the Takeda Agreement. Under the Takeda Commercial Supply Agreement, the Company will pay Takeda a fixed price per kilogram of relugolix drug substance through December 31, 2019. The Company has made and Takeda has accepted an initial firm order to supply relugolix drug substance to the Company through December 31, 2019. For relugolix drug substance manufactured or delivered on or after such date, the Company will pay Takeda a price per kilogram of relugolix drug substance to be agreed upon between the parties at the beginning of each fiscal year. In addition, under the Takeda Commercial Supply Agreement, Takeda has agreed to assist with the transfer of technology and Takeda manufacturing know-how to a second contract manufacturing organization of the Company’s subsidiary, Myovant Sciences GmbH. The Company has agreed to reimburse Takeda for all internal costs, and external costs, charges, and expenses, in each case, reasonably incurred by Takeda in connection with any technology transfer services. The initial term of the Takeda Commercial Supply Agreement began on May 30, 2018 and will continue for five years. At the end of the initial term, the Takeda Commercial Supply Agreement automatically renews for successive one-year terms, unless either party gives notice of termination to the other at least 12 months prior to the end of the then-current term. The Takeda Commercial Supply Agreement may be terminated by either party upon 90 days’ notice of an uncured material breach of its terms by the other party, or immediately upon notice to the other party of a party’s bankruptcy. Each party will also have the right to terminate the Takeda Commercial Supply Agreement, in whole or in part, for any reason upon 180 days’ prior written notice to the other party, provided that any then-open purchase orders, including the initial firm order for relugolix drug substance through December 31, 2019, will remain in effect and be binding on both parties. The Takeda Commercial Supply Agreement, including any then-open purchase order thereunder, will terminate immediately upon the termination of the Takeda Agreement in accordance with its terms. The Takeda Commercial Supply Agreement also includes customary provisions relating to, among others, delivery, inspection procedures, warranties, quality management, storage, handling and transport, intellectual property, confidentiality and indemnification.

Subsequent Events

(A) Private Placement with RSL

On April 2, 2018, the Company entered into a share purchase agreement, or the Purchase Agreement, with RSL pursuant to which the Company agreed to issue and sell to RSL 1,110,015 of its common shares at a purchase price of $20.27 per common share in a private placement, or the Private Placement. In April 2018, the Company received gross proceeds of $22.5 million from RSL at the closing of the Private Placement.

(B) At-the-Market Equity Offering Program

On April 2, 2018, the Company entered into a sales agreement, or the Sales Agreement, with Cowen and Company, LLC, or Cowen, to sell its common shares having an aggregate offering price of up to $100.0 million from time to time through an “at-the-market” equity offering program under which Cowen acts as the Company’s agent. In the first quarter of fiscal year 2018, the Company issued and sold 2,767,129 of its common shares under the Sales Agreement. The common shares were sold at a weighted-average-price of $21.47 per common share for aggregate net proceeds to the Company of approximately $57.6 million, after deducting commissions.

In May 2018, the Company entered into a Commercial Manufacturing and Supply Agreement with Takeda, or the Takeda Commercial Supply Agreement. Pursuant to the Takeda Commercial Supply Agreement, Takeda has agreed to supply the Company and the Company has agreed to obtain from Takeda certain quantities of relugolix drug substance according to agreed-upon quality specifications and in order to commercialize relugolix in accordance with the Takeda Agreement. Under the Takeda Commercial Supply Agreement, the Company will pay Takeda a fixed price per kilogram of relugolix drug substance through December 31, 2019. The Company has made and Takeda has accepted an initial firm order to supply relugolix drug substance to the Company through December 31, 2019. For relugolix drug substance manufactured or delivered on or after such date, the Company will pay Takeda a price per kilogram of relugolix drug substance to be agreed upon between the parties at the beginning of each fiscal year.

In addition, under the Takeda Commercial Supply Agreement, Takeda has agreed to assist with the transfer of technology and Takeda manufacturing know-how to a second contract manufacturing organization of the Company’s subsidiary, Myovant Sciences GmbH. The Company has agreed to reimburse Takeda for all internal costs, and external costs, charges, and expenses, in each case, reasonably incurred by Takeda in connection with any technology transfer services.

The initial term of the Takeda Commercial Supply Agreement began on May 30, 2018 and will continue for five years. At the end of the initial term, the Takeda Commercial Supply Agreement automatically renews for successive one-year terms, unless either party gives notice of termination to the other at least 12 months prior to the end of the then-current term. The Takeda Commercial Supply Agreement may be terminated by either party upon 90 days’ notice of an uncured material breach of its terms by the other party, or immediately upon notice to the other party of a party’s bankruptcy. Each party will also have the right to terminate the Takeda Commercial Supply Agreement, in whole or in part, for any reason upon 180 days’ prior written notice to the other party, provided that any then-open purchase orders, including the initial firm order for relugolix drug substance through December 31, 2019, will remain in effect and be binding on both parties. The Takeda Commercial Supply Agreement, including any then-open purchase order thereunder, will terminate immediately upon the termination of the Takeda Agreement in accordance with its terms.

The Takeda Commercial Supply Agreement also includes customary provisions relating to, among others, delivery, inspection procedures, warranties, quality management, storage, handling and transport, intellectual property, confidentiality and indemnification.