Modis Asset Acquisition and Assumption of License Agreements (Details) $ in Thousands			3 Months Ended	9 Months Ended
	Sep. 26, 2019 USD ($)	Sep. 06, 2019 USD ($) employee shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Asset Acquisition [Line Items]
Cash paid for asset acquisition				$ 175,732	$ 0
Fair value of shares issued			$ 68,124
Acquisition holdback amount placed in escrow			$ 25,000	$ 25,000		$ 0
Modis Acquisition
Asset Acquisition [Line Items]
Consideration paid		$ 246,500
Cash paid for asset acquisition		175,500
Transaction costs		3,500
Net working capital adjustment receivable		600
Acquisition holdback amount placed in escrow		$ 25,000
Royalty (percent)		5.00%
Fair value assigned to acquired MT1621		$ 244,500
Assumed net liabilities		$ 2,800
Number of former employees that continued employment with Zogenix | employee		13
Royalties payment period	15 years
Modis Acquisition | FDA Approval in US
Asset Acquisition [Line Items]
Contingent consideration to be paid		$ 100,000
Modis Acquisition | EMA Approval in Europe
Asset Acquisition [Line Items]
Contingent consideration to be paid		50,000
Modis Acquisition | Achievement of Regulatory Milestones | Columbia University
Asset Acquisition [Line Items]
Consideration payable upon achievement of milestones	$ 2,900
Modis Acquisition | Certain commercial milestone events
Asset Acquisition [Line Items]
Consideration payable upon achievement of milestones		10,000
Modis Acquisition | Certain commercial milestone events | Columbia University
Asset Acquisition [Line Items]
Consideration payable upon achievement of milestones	$ 25,000
Modis Acquisition | Research, development and regulatory milestones
Asset Acquisition [Line Items]
Consideration payable upon achievement of milestones		2,700
Modis Acquisition | Unvested awards
Asset Acquisition [Line Items]
Fair value of shares issued		$ 4,900
Common Stock
Asset Acquisition [Line Items]
Shares issued (shares) | shares			1,595,000
Fair value of shares issued			$ 2
Common Stock | Modis Acquisition
Asset Acquisition [Line Items]
Shares issued (shares) | shares		1,595,025
Fair value of shares issued		$ 68,100