Stock-based Compensation Expense - Weighted-Average Assumptions for Stock Options (Details) - Stock Option [Member] - Employee [Member]	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Stock-based Compensation Expense [Abstract]
Risk-free interest rate	3.90%	4.50%
Dividend yield	0.00%	0.00%
Volatility	43.10%	41.90%
Expected life	6 years 3 months 18 days	6 years 3 months 18 days

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

IONIS PHARMACEUTICALS INC 10-Q