Novartis Collaboration and License Agreement ("the Novartis Agreement") - Narrative (Details) - Novartis	3 Months Ended		6 Months Ended		12 Months Ended	42 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2019 USD ($) research	Jun. 30, 2022 USD ($)
Novartis Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Proceeds from upfront non-refundable license fee					$ 50,000,000.0
Revenue recognized from related party	$ 5,000,000	$ 1,800,000	$ 6,200,000	$ 4,000,000
Novartis Agreement | Achievement of First Patient Dosing Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Due from related parties	4,000,000		$ 4,000,000			$ 4,000,000
Revenue recognized from related party		$ 0		$ 0		$ 25,000,000
Novartis Agreement, R&D For PLN-1474 | Research and development expenses
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction price of Novartis agreement					20,000,000.0
Novartis Agreement, R&D For Integrin Research Targets | Research and development expenses
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction price of Novartis agreement					$ 16,800,000
Maximum | Novartis Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of Integrin research targets | research					3
Collaboration and license agreement, integrin research targets amount (up to)					$ 416,000,000.0
Amount remaining for achievement	$ 387,000,000.0