Defined Contribution Plan	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Defined Contribution Plan	Defined Contribution PlanThe Company sponsors a 401(k) retirement savings plan for the benefit of its employees, including Denali's named executive officers, who satisfy certain eligibility requirements. Under the 401(k) plan, eligible employees may elect to defer a portion of their compensation, within the limits prescribed by the Code, on a pre-tax or after-tax (Roth) basis through contributions to the 401(k) plan. The 401(k) plan authorizes employer safe harbor contributions. The 401(k) plan is intended to qualify under Sections 401(a) and 501(a) of the Code. As a tax-qualified retirement plan, pre-tax contributions to the 401(k) plan and earnings on those pre-tax contributions are not taxable to the employees until distributed from the 401(k) plan, and earnings on Roth contributions are not taxable when distributed from the 401(k) plan. The Company made contributions to the Plan for eligible participants, and recorded contribution expenses of $1.6 million, $0.9 million and $0.5 million for the years ended December 31, 2019, 2018, and 2017, respectively.