Long-term Debt - Summary of Credit Facility (Detail) - Credit Facility [Member] - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Principal	$ 375,000	$ 375,000
Less: debt discount and issuance costs	(14,465)	(15,511)
Net carrying amount	$ 360,535	$ 359,489

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References + Details

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References

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+ Details

Apellis Pharmaceuticals, Inc. 10-Q