Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section S99
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Related Party Transactions - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Novartis International Pharmaceutical Ltd.
Related Party Transaction [Line Items]
Payments to related parties	$ 0	$ 0	$ 2,500,000	$ 0	$ 900,000
Silverstein Foundation \| Funding Agreement
Related Party Transaction [Line Items]
Fund received from related parties	$ 0	$ 0	$ 0	$ 500,000	$ 0
Common Stock
Related Party Transaction [Line Items]
Issuance of common shares to PureTech, shares					1,886,363