Collaboration and License Agreement - Additional Information (Details)		1 Months Ended	12 Months Ended
	Jul. 28, 2017 USD ($)	Nov. 30, 2017 USD ($) Target CandidateorProduct	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from issuance of shares of preferred stock	$ 83,500,000
Collaboration agreement revenue recognized			$ 3,684,000
Novartis
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront, nonrefundable payment received		$ 35,000,000
Collaborative agreement target fee		$ 5,000,000
Collaboration agreement, research term		5 years
Allocated to collaboration agreement		$ 33,300,000
Upfront nonrefundable consideration allocated to combined unit of accounting		$ 33,300,000
Novartis | Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition on straight-line basis over estimated period of performance for combined unit of accounting		10 years
Collaboration agreement revenue recognized			3,700,000	$ 0
Deferred revenue			33,200,000
Novartis | Collaboration Agreement | Prepaid Expenses and Other Current Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Receivable			$ 800,000
Novartis | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets selected | Target		4
Number of targets during research term | Target		4
Collaboration agreement number of candidates or products for develop and commercialize | CandidateorProduct		4
Collaboration agreement eligible milestone payments eligible to receive		$ 530,000,000
Collaboration agreement eligible development milestone payments eligible to receive		180,000,000
Collaboration agreement eligible regulatory milestone payments eligible to receive		170,000,000
Collaboration agreement eligible commercial milestone payments eligible to receive		180,000,000
Novartis | Series B Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront, nonrefundable payment received		1,700,000
Proceeds from issuance of shares of preferred stock		10,000,000
Preferred stock estimated fair value		$ 11,700,000