Basis of Presentation (Details) (Maximum)	9 Months Ended	1 Months Ended
Sep. 30, 2012	Oct. 31, 2012 Regulus Therapeutics Inc.
Investments
Ownership percentage after stock sale	20.00%	20.00%

The ownership percentage represented by the entity's equity investments in companies with which it conducts business and which are not accounted for under the equity method of accounting.

No definition available.

Name:	isis_EquityInvestmentsOtherThanEquityMethodOwnershipPercentage
Namespace Prefix:	isis_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration