The spot exchange rate at the end of the reporting period. Exchange rate is the ratio of exchange for two currencies. Spot exchange rate is the exchange rate for immediate delivery.

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Financial Risk Management Objectives and Policies - Summary of Sensitivity Analysis of Foreign Currency Risk (Detail) € in Thousands	12 Months Ended
	Dec. 31, 2020 EUR (€)	Dec. 31, 2019	Dec. 31, 2018
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	0.8149	0.8902	0.8738
Euro weakens by 1% against U.S. dollars [Member] \| Immatics GmbH [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.2394
Profit/(loss)	€ (757)
Carrying amount	€ 75,706
Euro weakens by 1% against U.S. dollars [Member] \| Immatics N.V. [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.2394
Profit/(loss)	€ (421)
Carrying amount	€ 42,107
Euro strengths by 1% against U.S. dollars [Member] \| Immatics GmbH [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.2148
Profit/(loss)	€ 772
Carrying amount	€ 77,235
Euro strengths by 1% against U.S. dollars [Member] \| Immatics N.V. [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.2148
Profit/(loss)	€ 430
Carrying amount	€ 42,958
Euro weakens by 5% against U.S. dollars [Member] \| Immatics GmbH [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.2885
Profit/(loss)	€ (3,641)
Carrying amount	€ 72,822
Euro weakens by 5% against U.S. dollars [Member] \| Immatics N.V. [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.2885
Profit/(loss)	€ (2,025)
Carrying amount	€ 40,503
Euro strengths by 5% against U.S. dollars [Member] \| Immatics GmbH [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.1657
Profit/(loss)	€ 4,024
Carrying amount	€ 80,487
Euro strengths by 5% against U.S. dollars [Member] \| Immatics N.V. [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.1657
Profit/(loss)	€ 2,238
Carrying amount	€ 44,766
Euro weakens by 10% against U.S. dollars [Member] \| Immatics GmbH [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.3498
Profit/(loss)	€ (6,951)
Carrying amount	€ 69,512
Euro weakens by 10% against U.S. dollars [Member] \| Immatics N.V. [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.3498
Profit/(loss)	€ (3,866)
Carrying amount	€ 38,662
Euro strengths by 10% against U.S. dollars [Member] \| Immatics GmbH [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.1044
Profit/(loss)	€ 8,496
Carrying amount	€ 84,959
Euro strengths by 10% against U.S. dollars [Member] \| Immatics N.V. [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Conversion rate	1.1044
Profit/(loss)	€ 4,725
Carrying amount	€ 47,253