Novartis Collaboration and License Agreement ("the Novartis Agreement") - Narrative (Details) - Novartis	3 Months Ended		12 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2019 USD ($) research
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	$ 1,200,000	$ 2,200,000
Novartis Agreement | Achievement of First Patient Dosing Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized from related party	$ 0	$ 0	25,000,000.0
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			$ 13,800,000
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			$ 391,000,000.0