Subsequent Events	12 Months Ended
Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventOn January 18, 2022, we entered into a definitive agreement and plan of merger (the Merger Agreement) with UCB S.A., a société anonyme formed under the laws of Belgium (UCB) and its subsidiary, Zinc Merger Sub, Inc., a Delaware corporation (Purchaser) pursuant to which, among other things, Purchaser will be merged with and into Zogenix (the Merger), with Zogenix surviving the Merger as a wholly-owned subsidiary of UCB, subject to the terms and conditions of the Merger Agreement. Under the terms of the Merger Agreement, and upon the terms and subject to the conditions thereof, Purchaser commenced a tender offer to purchase all of the outstanding common shares of Zogenix for (i) $26.00 per share in cash, without interest and less any applicable tax withholding, plus (ii) one non-transferrable contingent value right per common share representing the right to receive a contingent payment of $2.00 in cash, without interest and less any applicable tax withholding, which amount will become payable, if at all, if a specified milestone is achieved on or prior to December 31, 2023. The boards of directors of both Zogenix and UCB have unanimously approved the transaction.The obligation of UCB and Purchaser to consummate the tender offer is subject to the tender of a majority of our outstanding common shares in the Offer and other customary conditions. If these conditions are satisfied and the tender offer closes, Purchaser will acquire any remaining shares through a merger pursuant to section 251(h) of the Delaware General Corporate Law. The completion of the Merger is subject to customary conditions, including, among others, the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, the absence of any order or law that has the effect of enjoining or otherwise prohibiting the completion of the Merger, each party’s representations and warranties being true and correct as of the closing, generally to a “Material Adverse Effect” standard. The Merger Agreement provides for a termination fee of $59.0 million payable by us under certain circumstances, including if we terminate the Merger Agreement to accept a superior proposal and enter into a definitive written agreement with respect to such proposal

Subsequent Events

12 Months Ended

Dec. 31, 2021

Subsequent EventOn January 18, 2022, we entered into a definitive agreement and plan of merger (the Merger Agreement) with UCB S.A., a société anonyme formed under the laws of Belgium (UCB) and its subsidiary, Zinc Merger Sub, Inc., a Delaware corporation (Purchaser) pursuant to which, among other things, Purchaser will be merged with and into Zogenix (the Merger), with Zogenix surviving the Merger as a wholly-owned subsidiary of UCB, subject to the terms and conditions of the Merger Agreement. Under the terms of the Merger Agreement, and upon the terms and subject to the conditions thereof, Purchaser commenced a tender offer to purchase all of the outstanding common shares of Zogenix for (i) $26.00 per share in cash, without interest and less any applicable tax withholding, plus (ii) one non-transferrable contingent value right per common share representing the right to receive a contingent payment of $2.00 in cash, without interest and less any applicable tax withholding, which amount will become payable, if at all, if a specified milestone is achieved on or prior to December 31, 2023. The boards of directors of both Zogenix and UCB have unanimously approved the transaction.The obligation of UCB and Purchaser to consummate the tender offer is subject to the tender of a majority of our outstanding common shares in the Offer and other customary conditions. If these conditions are satisfied and the tender offer closes, Purchaser will acquire any remaining shares through a merger pursuant to section 251(h) of the Delaware General Corporate Law. The completion of the Merger is subject to customary conditions, including, among others, the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, the absence of any order or law that has the effect of enjoining or otherwise prohibiting the completion of the Merger, each party’s representations and warranties being true and correct as of the closing, generally to a “Material Adverse Effect” standard. The Merger Agreement provides for a termination fee of $59.0 million payable by us under certain circumstances, including if we terminate the Merger Agreement to accept a superior proposal and enter into a definitive written agreement with respect to such proposal