Cash, cash equivalents, short-term investments and restricted cash - Summary of Unrealized Gains and Losses (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2021 USD ($) investment	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) investment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, realized gain (loss)	$ 0	$ 0	$ 0	$ 0
Debt securities, available-for-sale, impairment losses	$ 0	$ 0	$ 0	$ 0
Debt securities, unrealized loss position, 12 months or longer \| investment	0		0
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 27,674,000		$ 27,674,000		$ 27,669,000
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	27,674,000		27,674,000		27,669,000
Gross Unrealized Gains	0		0		0
Gross Unrealized Loss	0		0		0
Fair Value	$ 27,674,000		$ 27,674,000		$ 27,669,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI).

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