Ionis Pharmaceuticals (IONS) 10-Q 5 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 30, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	ISIS PHARMACEUTICALS INC
Entity Central Index Key	874015
Document Type	10-Q
Document Period End Date	31-Mar-15
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		119,713,341
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$148,348	$142,998
Short-term investments	546,706	585,834
Contracts receivable	26,934	3,903
Inventories	6,839	6,290
Investment in Regulus Therapeutics Inc.	93,446	81,881
Other current assets	13,154	15,691
Total current assets	835,427	836,597
Property, plant and equipment, net	89,047	88,958
Licenses, net	2,221	2,690
Patents, net	17,915	17,186
Deposits and other assets	10,823	10,378
Total assets	955,433	955,809
Current liabilities:
Accounts payable	16,487	17,984
Accrued compensation	5,411	12,302
Accrued liabilities	23,746	30,451
Current portion of long-term obligations	2,058	2,882
Current portion of deferred contract revenue	52,586	51,713
Total current liabilities	100,288	115,332
Long-term deferred contract revenue	119,083	127,797
Long-term obligations, less current portion	7,510	7,669
Long-term financing liability for leased facility	71,848	71,731
Total liabilities	679,582	698,029
Stockholders' equity:
Common stock, $0.001 par value; 300,000,000 shares authorized, 119,602,322 and 118,442,726 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	120	118
Additional paid-in capital	1,251,928	1,224,509
Accumulated other comprehensive income	47,114	39,747
Accumulated deficit	-1,023,311	-1,006,594
Total stockholders' equity	275,851	257,780
Total liabilities and stockholders' equity	955,433	955,809
1 Percent Convertible Senior Notes [Member]
Current liabilities:
Convertible senior notes	332,274	327,486
2 3/4 Percent Convertible Senior Notes [Member]
Current liabilities:
Convertible senior notes	$48,579	$48,014

CONDENSED_CONSOLIDATED_BALANCE1

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Stockholders' equity:
Common stock, par value (in dollars per share)	0.001	0.001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	119,602,322	118,442,726
Common stock, shares outstanding (in shares)	119,602,322	118,442,726
1 Percent Convertible Senior Notes [Member]
LIABILITIES AND STOCKHOLDERS' EQUITY
Interest rate on convertible senior notes (in hundredths)	1.00%	1.00%
2 3/4 Percent Convertible Senior Notes [Member]
LIABILITIES AND STOCKHOLDERS' EQUITY
Interest rate on convertible senior notes (in hundredths)	2.75%	2.75%

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenue:
Research and development revenue under collaborative agreements	$61,892	$19,550
Licensing and royalty revenue	691	8,611
Total revenue	62,583	28,161
Expenses:
Research, development and patent expenses	64,447	53,448
General and administrative	7,466	4,380
Total operating expenses	71,913	57,828
Loss from operations	-9,330	-29,667
Other income (expense):
Investment income	845	657
Interest expense	-9,021	-4,943
Gain on investments, net	0	397
Loss before income tax benefit	-17,506	-33,556
Income tax benefit	789	2,276
Net loss	($16,717)	($31,280)
Basic and diluted net loss per share (in dollars per share)	($0.14)	($0.27)
Shares used in computing basic and diluted net loss per share	118,948	117,128

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) [Abstract]
Net loss	($16,717)		($31,280)
Unrealized gains on securities, net of tax	7,367		8,261
Reclassification adjustment for realized gains included in net loss	0	[1]	-341	[1]
Comprehensive loss	($9,350)		($23,360)
[1]	Included in gain on investments, net on our condensed consolidated statement of operations.

CONDENSED_CONSOLIDATED_STATEME2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating activities:
Net loss	($16,717)	($31,280)
Adjustments to reconcile net loss to net cash (used in) operating activities:
Depreciation	1,571	1,561
Amortization of patents	312	263
Amortization of licenses	469	471
Amortization of premium on investments, net	1,749	1,376
Amortization of debt issuance costs	275	135
Amortization of long-term financing liability for leased facility	1,662	1,652
Stock-based compensation expense	13,305	7,069
Gain on investments, net	0	-397
Non-cash losses related to patents, licensing and property, plant and equipment	93	108
Tax benefit from other unrealized gains on securities	-798	-2,276
Changes in operating assets and liabilities:
Contracts receivable	-23,031	1,279
Inventories	-549	496
Other current and long-term assets	-2,451	-896
Accounts payable	-2,695	-2,646
Accrued compensation	-6,891	-7,840
Deferred rent	62	25
Accrued liabilities	-6,704	2,643
Deferred contract revenue	-7,841	-5,742
Net cash (used in) operating activities	-42,826	-32,328
Investing activities:
Purchases of short-term investments	-40,213	-69,185
Proceeds from the sale of short-term investments	78,460	95,288
Purchases of property, plant and equipment	-878	-1,403
Acquisition of licenses and other assets, net	-719	-333
Proceeds from the sale of strategic investments	0	454
Net cash provided by investing activities	36,650	24,821
Financing activities:
Proceeds from equity awards	14,116	12,003
Principal payments on debt and capital lease obligations	-2,590	-2,691
Net cash provided by financing activities	11,526	9,312
Net increase in cash and cash equivalents	5,350	1,805
Cash and cash equivalents at beginning of period	142,998	159,973
Cash and cash equivalents at end of period	148,348	161,778
Supplemental disclosures of cash flow information:
Interest paid	37	83
Supplemental disclosures of non-cash investing and financing activities:
Amounts accrued for capital and patent expenditures	1,198	1,506
2 3/4 Percent Convertible Senior Notes [Member]
Adjustments to reconcile net loss to net cash (used in) operating activities:
Amortization of convertible notes discount	565	1,671
1 Percent Convertible Senior Notes [Member]
Adjustments to reconcile net loss to net cash (used in) operating activities:
Amortization of convertible notes discount	$4,788	$0

CONDENSED_CONSOLIDATED_STATEME3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (Parenthetical)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
1 Percent Convertible Senior Notes [Member]
Adjustments to reconcile net loss to net cash (used in) operating activities:
Interest rate on convertible notes (in hundredths)	1.00%	1.00%
2 3/4 Percent Convertible Senior Notes [Member]
Adjustments to reconcile net loss to net cash (used in) operating activities:
Interest rate on convertible notes (in hundredths)	2.75%	2.75%	2.75%

Basis_of_Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2015
Basis of Presentation [Abstract]
Basis of Presentation		1	Basis of Presentation
	The unaudited interim condensed consolidated financial statements for the three months ended March 31, 2015 and 2014 have been prepared on the same basis as the audited financial statements for the year ended December 31, 2014. The financial statements include all normal recurring adjustments, which we consider necessary for a fair presentation of our financial position at such dates and our operating results and cash flows for those periods. Results for the interim periods are not necessarily indicative of the results for the entire year. For more complete financial information, these financial statements, and notes thereto, should be read in conjunction with the audited financial statements for the year ended December 31, 2014 included in our Annual Report on Form 10-K filed with the Securities and Exchange Commission, or SEC.
	The condensed consolidated financial statements include the accounts of Isis Pharmaceuticals, Inc. ("we", "us" or "our") and our wholly owned subsidiary, Akcea Therapeutics, Inc., which we formed in December 2014.

Significant_Accounting_Policie

Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Significant Accounting Policies [Abstract]
Significant Accounting Policies		2	Significant Accounting Policies
	Revenue Recognition
	We generally recognize revenue when we have satisfied all contractual obligations and are reasonably assured of collecting the resulting receivable. We are often entitled to bill our customers and receive payment from our customers in advance of recognizing the revenue. In the instances in which we have received payment from our customers in advance of recognizing revenue, we include the amounts in deferred revenue on our consolidated balance sheet.
	Arrangements with multiple deliverables
	Our collaboration agreements typically contain multiple elements, or deliverables, including technology licenses or options to obtain technology licenses, research and development services, and in certain cases manufacturing services, and we allocate the consideration to each unit of accounting based on the relative selling price of each deliverable.
	Identifying deliverables and units of accounting
	We evaluate the deliverables in our collaboration agreements to determine whether they meet the criteria to be accounted for as separate units of accounting or whether they should be combined with other deliverables and accounted for as a single unit of accounting. When the delivered items in an arrangement have "stand-alone value" to our customer, we account for the deliverables as separate units of accounting. For example, in December 2012, we entered into a global collaboration agreement with AstraZeneca to discover and develop antisense drugs against five cancer targets. As part of the collaboration, we received a $25 million upfront payment in December 2012 and a $6 million payment in June 2013 when AstraZeneca elected to continue the research collaboration. We are also eligible to receive milestone payments, license fees for the research program targets and royalties on any product sales of drugs resulting from this collaboration. In exchange, we granted AstraZeneca an exclusive license to develop and commercialize ISIS-STAT3-2.5Rx and ISIS-AR-2.5Rx. We also granted AstraZeneca options to license up to three cancer drugs under the separate research program. We were responsible for completing IND-enabling studies for ISIS-AR-2.5Rx, which we completed in early 2014. We were also responsible for completing an ongoing clinical study of ISIS-STAT3-2.5Rx, which we substantially completed in the first quarter of 2015. AstraZeneca is responsible for all other global development, regulatory and commercialization activities for ISIS-STAT3-2.5Rx and ISIS-AR-2.5Rx. In addition, if AstraZeneca exercises its option for any drugs resulting from the research program, AstraZeneca will assume global development, regulatory and commercialization responsibilities for such drug. Since this agreement has multiple elements, we evaluated the deliverables in this arrangement when we entered into the agreement and determined that certain deliverables, either individually or in combination, have stand-alone value. Below is a list of the four separate units of accounting under our agreement:
			The exclusive license we granted to AstraZeneca to develop and commercialize ISIS-STAT3-2.5Rx for the treatment of cancer;
			The development services we agreed to perform for ISIS-STAT3-2.5Rx;
			The exclusive license we granted to AstraZeneca to develop and commercialize ISIS-AR-2.5Rx and the research services we performed for ISIS-AR-2.5Rx; and
			The option to license up to three drugs under a research program and the research services we are performing for this program.
	Measurement and allocation of arrangement consideration
	Our collaborations may provide for various types of payments to us including upfront payments, funding of research and development, milestone payments, licensing fees, profit sharing and royalties on product sales. We initially allocate the amount of consideration that is fixed and determinable at the time the agreement is entered into and exclude contingent consideration. We allocate the consideration to each unit of accounting based on the relative selling price of each deliverable. Delivered items have stand-alone value if they are sold separately by any vendor or the customer could resell the delivered items on a stand-alone basis. We use the following hierarchy of values to estimate the selling price of each deliverable: (i) vendor-specific objective evidence of fair value; (ii) third-party evidence of selling price; and (iii) best estimate of selling price, or BESP. The BESP reflects our best estimate of what the selling price would be if we regularly sold the deliverable on a stand-alone basis. We recognize the revenue allocated to each unit of accounting as we deliver the related goods or services. If we determine that we should treat certain deliverables as a single unit of accounting, then we recognize the revenue ratably over our estimated period of performance.
	We determined that the ISIS-STAT3-2.5Rx license had stand-alone value because it is an exclusive license that gives AstraZeneca the right to develop ISIS-STAT3-2.5Rx or to sublicense its rights. In addition, ISIS-STAT3-2.5Rx is currently in development and it is possible that AstraZeneca or another third party could conduct clinical trials without assistance from us. As a result, we considered the ISIS-STAT3-2.5Rx license and the development services for ISIS-STAT3-2.5Rx to be separate units of accounting. We recognized the portion of the consideration allocated to the ISIS-STAT3-2.5Rx license immediately because we delivered the license and earned the revenue. We recognized as revenue the amount allocated to the development services for ISIS-STAT3-2.5Rx over the period of time we performed services. The ISIS-AR-2.5Rx license is also an exclusive license. At the inception of the agreement, ISIS-AR-2.5Rx was in an early stage of research. Therefore, we concluded that our knowledge and expertise with antisense technology was essential for AstraZeneca or another third party to successfully develop ISIS-AR-2.5Rx. As a result, we determined that the ISIS-AR-2.5Rx license did not have stand-alone value and we combined the ISIS-AR-2.5Rx license and related research services into one unit of accounting. We recognized revenue for the combined unit of accounting over the period of time we performed services, which ended in the first quarter of 2014. We determined that the options under the research program did not have stand-alone value because AstraZeneca cannot develop or commercialize drugs resulting from the research program until AstraZeneca exercises the respective option or options. As a result, we considered the research options and the related research services as a combined unit of accounting. We are recognizing revenue for the combined unit of accounting over the period of our performance.
	We determined that the allocable arrangement consideration was $31 million and we allocated it based on the relative BESP of each unit of accounting. We engaged a third party, independent valuation expert to assist us with determining BESP. We estimated the selling price of the licenses granted for ISIS-STAT3-2.5Rx and ISIS-AR-2.5Rx by using the relief from royalty method. Under this method, we estimated the amount of income, net of taxes, for each drug. We then discounted the projected income for each license to present value. The significant inputs we used to determine the projected income of the licenses included:
			Estimated future product sales;
			Estimated royalties on future product sales;
			Contractual milestone payments;
			Expenses we expect to incur;
			Income taxes; and
			An appropriate discount rate.
	We estimated the selling price of the research and development services by using our internal estimates of the cost to perform the specific services, marked up to include a reasonable profit margin, and estimates of expected cash outflows to third parties for services and supplies over the expected period that we will perform research and development. The significant inputs we used to determine the selling price of the research and development services included:
			The number of internal hours we will spend performing these services;
			The estimated number and cost of studies we will perform;
			The estimated number and cost of studies that we will contract with third parties to perform; and
			The estimated cost of drug product we will use in the studies.
	Timing of revenue recognition
	We recognize revenue over the period of our performance for each deliverable when we determine that it is realized or realizable and earned. Typically, we must estimate our period of performance when the agreements we enter into do not clearly define such information. Our collaborative agreements typically include a research and/or development project plan outlining the activities the agreement requires each party to perform during the collaboration. We estimate the period of time over which we will complete the activities for which we are responsible and use that period of time as our period of performance for purposes of revenue recognition and recognize revenue ratably over such period. We have made estimates of our continuing obligations under numerous agreements and in certain instances the timing of satisfying these obligations may change as the development plans for our drugs progress. Accordingly, our estimates may change in the future. If our estimates and judgments change over the course of these agreements, it may affect the timing and amount of revenue that we recognize in future periods.
	Multiple agreements
	From time to time, we may enter into separate agreements at or near the same time with the same customer. We evaluate such agreements to determine whether they should be accounted for individually as distinct arrangements or whether the separate agreements are, in substance, a single multiple element arrangement. We evaluate whether the negotiations are conducted jointly as part of a single negotiation, whether the deliverables are interrelated or interdependent, whether fees in one arrangement are tied to performance in another arrangement, and whether elements in one arrangement are essential to another arrangement. Our evaluation involves significant judgment to determine whether a group of agreements might be so closely related that they are, in effect, part of a single arrangement. For example, since early 2012 we have entered into four collaboration agreements with Biogen:
			In January 2012, we entered into a collaboration agreement with Biogen to develop and commercialize ISIS-SMNRx for spinal muscular atrophy, or SMA. As part of the collaboration, we received a $29 million upfront payment and we are responsible for global development of ISIS-SMNRx through completion of Phase 2/3 clinical trials.
			In June 2012, we entered into a second and separate collaboration agreement with Biogen to develop and commercialize a novel antisense drug targeting DMPK, or dystrophia myotonica-protein kinase. As part of the collaboration, we received a $12 million upfront payment and we are responsible for global development of the drug through the completion of a Phase 2 clinical trial.
			In December 2012, we entered into a third and separate collaboration agreement with Biogen to discover and develop antisense drugs against three targets to treat neurological or neuromuscular disorders. As part of the collaboration, we received $30 million upfront payment and we are responsible for the discovery of a lead antisense drug for each of three targets.
			In September 2013, we entered into a fourth and separate collaboration agreement with Biogen to leverage antisense technology to advance the treatment of neurological diseases. We granted Biogen exclusive rights to the use of our antisense technology to develop therapies for neurological diseases as part of this broad collaboration. We received a $100 million upfront payment and we are responsible for discovery and early development through the completion of a Phase 2 clinical trial for each antisense drug identified during the six year term of this collaboration, while Biogen is responsible for the creation and development of small molecule treatments and biologics.
	All four of these collaboration agreements give Biogen the option to license one or more drugs resulting from the specific collaboration. If Biogen exercises an option, it will pay us a license fee and will assume future development, regulatory and commercialization responsibilities for the licensed drug. We are also eligible to receive milestone payments associated with the research and/or development of the drugs prior to licensing, milestone payments if Biogen achieves pre-specified regulatory milestones, and royalties on any product sales of drugs resulting from these collaborations.
	We evaluated all four of the Biogen agreements to determine whether we should account for them as separate agreements. We determined that we should account for the agreements separately because we conducted the negotiations independently of one another, each agreement focuses on different drugs, there are no interrelated or interdependent deliverables, there are no provisions in any of these agreements that are essential to the other agreement, and the payment terms and fees under each agreement are independent of each other. We also evaluated the deliverables in each of these agreements to determine whether they met the criteria to be accounted for as separate units of accounting or whether they should be combined with other deliverables and accounted for as a single unit of accounting. For all four of these agreements, we determined that the options did not have stand-alone value because Biogen cannot pursue the development or commercialization of the drugs resulting from these collaborations until it exercises the respective option or options. As such, for each agreement we considered the deliverables to be a single unit of accounting and we are recognizing the upfront payment for each of the agreements over the respective estimated period of our performance.
	Milestone payments
	Our collaborations often include contractual milestones, which typically relate to the achievement of pre-specified development, regulatory and commercialization events. These three categories of milestone events reflect the three stages of the life-cycle of our drugs, which we describe in more detail in the following paragraph.
	Prior to the first stage in the life-cycle of our drugs, we perform a significant amount of work using our proprietary antisense technology to design chemical compounds that interact with specific genes that are good targets for drug discovery. From these research efforts, we hope to identify a development candidate. The designation of a development candidate is the first stage in the life-cycle of our drugs. A development candidate is a chemical compound that has demonstrated the necessary safety and efficacy in preclinical animal studies to warrant further study in humans.
	During the first step of the development stage, we or our partners study our drugs in IND-enabling studies, which are animal studies intended to support an Investigational New Drug, or IND, application and/or the foreign equivalent. An approved IND allows us or our partners to study our development candidate in humans. If the regulatory agency approves the IND, we or our partners initiate Phase 1 clinical trials in which we typically enroll a small number of healthy volunteers to ensure the development candidate is safe for use in patients. If we or our partners determine that a development candidate is safe based on the Phase 1 data, we or our partners initiate Phase 2 studies that are generally larger scale studies in patients with the primary intent of determining the efficacy of the development candidate.
	The final step in the development stage is Phase 3 studies to gather the necessary safety and efficacy data to request marketing approval from the Food and Drug Administration, or FDA, and/or foreign equivalents. The Phase 3 studies typically involve large numbers of patients and can take up to several years to complete. If the data gathered during the trials demonstrates acceptable safety and efficacy results, we or our partner will submit an application to the FDA and/or its foreign equivalents for marketing approval. This stage of the drug’s life-cycle is the regulatory stage.
	If a drug achieves marketing approval, it moves into the commercialization stage, during which our partner will market and sell the drug to patients. Although our partner will ultimately be responsible for marketing and selling the partnered drug, our efforts to discover and develop a drug that is safe, effective and reliable contributes significantly to our partner’s ability to successfully sell the drug. The FDA and its foreign equivalents have the authority to impose significant restrictions on an approved drug through the product label and on advertising, promotional and distribution activities. Therefore, our efforts designing and executing the necessary animal and human studies are critical to obtaining claims in the product label from the regulatory agencies that would allow us or our partner to successfully commercialize our drug. Further, the patent protection afforded our drugs as a result of our initial patent applications and related prosecution activities in the United States and foreign jurisdictions are critical to our partner’s ability to sell our drugs without competition from generic drugs. The potential sales volume of an approved drug is dependent on several factors including the size of the patient population, market penetration of the drug, and the price charged for the drug.
	Generally, the milestone events contained in our partnership agreements coincide with the progression of our drugs from development, to regulatory approval and then to commercialization. The process of successfully discovering a new development candidate, having it approved and ultimately sold for a profit is highly uncertain. As such, the milestone payments we may earn from our partners involve a significant degree of risk to achieve. Therefore, as a drug progresses through the stages of its life-cycle, the value of the drug generally increases.
	Development milestones in our partnerships may include the following types of events:
			Designation of a development candidate. Following the designation of a development candidate, IND-enabling animal studies for a new development candidate generally take 12 to 18 months to complete;
			Initiation of a Phase 1 clinical trial. Generally, Phase 1 clinical trials take one to two years to complete;
			Initiation or completion of a Phase 2 clinical trial. Generally, Phase 2 clinical trials take one to three years to complete;
			Initiation or completion of a Phase 3 clinical trial. Generally, Phase 3 clinical trials take two to four years to complete.
	Regulatory milestones in our partnerships may include the following types of events:
			Filing of regulatory applications for marketing approval such as a New Drug Application, or NDA, in the United States or a Marketing Authorization Application, or MAA, in Europe. Generally, it takes six to twelve months to prepare and submit regulatory filings.
			Marketing approval in a major market, such as the United States, Europe or Japan. Generally it takes one to two years after an application is submitted to obtain approval from the applicable regulatory agency.
	Commercialization milestones in our partnerships may include the following types of events
			First commercial sale in a particular market, such as in the United States or Europe.
			Product sales in excess of a pre-specified threshold, such as annual sales exceeding $1 billion. The amount of time to achieve this type of milestone depends on several factors including but not limited to the dollar amount of the threshold, the pricing of the product and the pace at which customers begin using the product.
	We assess whether a substantive milestone exists at the inception of our agreements. When a substantive milestone is achieved, we recognize revenue related to the milestone payment immediately. For our existing licensing and collaboration agreements in which we are involved in the discovery and/or development of the related drug or provide the partner with access to new technologies we discover, we have determined that the majority of future development, regulatory and commercialization milestones are substantive. For example, we consider most of the milestones associated with our strategic alliance with Biogen substantive because we are using our antisense drug discovery platform to discover and develop new drugs against targets for neurological diseases. Alternatively, we consider milestones associated with our strategic alliance with Alnylam Pharmaceuticals, Inc. substantive because we provide Alnylam ongoing access to our technology to develop and commercialize RNA interference, or RNAi, therapeutics. In evaluating if a milestone is substantive we consider whether:
			Substantive uncertainty exists as to the achievement of the milestone event at the inception of the arrangement;
			The achievement of the milestone involves substantive effort and can only be achieved based in whole or in part on our performance or the occurrence of a specific outcome resulting from our performance;
			The amount of the milestone payment appears reasonable either in relation to the effort expended or to the enhancement of the value of the delivered items;
			There is no future performance required to earn the milestone; and
			The consideration is reasonable relative to all deliverables and payment terms in the arrangement.
	If any of these conditions are not met, we do not consider the milestone to be substantive and we defer recognition of the milestone payment and recognize it as revenue over our estimated period of performance, if any. Further information about our collaborative arrangements can be found in Note 6, Collaborative Arrangements and Licensing Agreements.
	Licensing and royalty revenue
	We often enter into agreements to license our proprietary patent rights on an exclusive or non-exclusive basis in exchange for license fees and/or royalties. We generally recognize as revenue immediately those licensing fees and royalties for which we have no significant future performance obligations and are reasonably assured of collecting the resulting receivable. For example, in the first quarter of 2014, we recognized $7.7 million in revenue from Alnylam related to its license of our technology to one of its partners because we had no performance obligations and collectability was reasonably assured.
	Cash, cash equivalents and short-term investments
We consider all liquid investments with maturities of three months or less when we purchase them to be cash equivalents. Our short-term investments have initial maturities of greater than three months from date of purchase. We classify our short-term investments as “available-for-sale” and carry them at fair market value based upon prices for identical or similar items on the last day of the fiscal period. We record unrealized gains and losses as a separate component of comprehensive income (loss) and include net realized gains and losses in gain (loss) on investments. We use the specific identification method to determine the cost of securities sold.
We have equity investments in privately- and publicly-held biotechnology companies that we have received as part of a technology license or collaboration agreement. At March 31, 2015 we held ownership interests of less than 20 percent in each of the respective companies.
We account for our equity investments in publicly-held companies at fair value and record unrealized gains and losses related to temporary increases and decreases in the stock of these publicly-held companies as a separate component of comprehensive income (loss). We account for equity investments in privately-held companies under the cost method of accounting because we own less than 20 percent and do not have significant influence over their operations. We hold one cost method investment in Atlantic Pharmaceuticals Limited. Realization of our equity position in this company is uncertain. When realization of our investment is uncertain, we record a full valuation allowance. In determining if and when a decrease in market value below our cost in our equity positions is temporary or other-than-temporary, we examine historical trends in the stock price, the financial condition of the company, near term prospects of the company and our current need for cash. If we determine that a decline in value in either a public or private investment is other-than-temporary, we recognize an impairment loss in the period in which the other-than-temporary decline occurs.
Inventory valuation
We capitalize the costs of raw materials that we purchase for use in producing our drugs because until we use these raw materials they have alternative future uses. We include in inventory raw material costs for drugs that we manufacture for our partners under contractual terms and that we use primarily in our clinical development activities and drug products. We can use each of our raw materials in multiple products and, as a result, each raw material has future economic value independent of the development status of any single drug. For example, if one of our drugs failed, we could use the raw materials for that drug to manufacture our other drugs. We expense these costs when we deliver the drugs to our partners, or as we provide these drugs for our own clinical trials. We reflect our inventory on the balance sheet at the lower of cost or market value under the first-in, first-out method. We review inventory periodically and reduce the carrying value of items we consider to be slow moving or obsolete to their estimated net realizable value. We consider several factors in estimating the net realizable value, including shelf life of raw materials, alternative uses for our drugs and clinical trial materials, and historical write-offs. We did not record any inventory write-offs for the three months ended March 31, 2015 and 2014. Total inventory, which consisted of raw materials, was $6.8 million and $6.3 million as of March 31, 2015 and December 31, 2014, respectively.
Research, development and patent expenses
Our research and development expenses include wages, benefits, facilities, supplies, external services, clinical trial and manufacturing costs and other expenses that are directly related to our research and development operations. We expense research and development costs as we incur them. When we make payments for research and development services prior to the services being rendered, we record those amounts as prepaid assets on our condensed consolidated balance sheet and we expense them as the services are provided.
We capitalize costs consisting principally of outside legal costs and filing fees related to obtaining patents. We amortize patent costs over the useful life of the patent, beginning with the date the United States Patent and Trademark Office, or foreign equivalent, issues the patent. We review our capitalized patent costs regularly to ensure that they include costs for patents and patent applications that have future value. We evaluate patents and patent applications that we are not actively pursuing and write off any associated costs.
Long-lived assets
We evaluate long-lived assets, which include property, plant and equipment, patent costs, and exclusive licenses acquired from third parties, for impairment on at least a quarterly basis and whenever events or changes in circumstances indicate that we may not be able to recover the carrying amount of such assets.
Use of estimates
The preparation of condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ from those estimates.
Basic and diluted net loss per share
We compute basic net loss per share by dividing the net loss by the weighted-average number of common shares outstanding during the period. As we incurred a net loss for the three months ended March 31, 2015 and 2014, we did not include dilutive common equivalent shares in the computation of diluted net loss per share because the effect would have been anti-dilutive. Common stock from the following would have had an anti-dilutive effect on net loss per share:
		1 percent convertible senior notes;
		2¾ percent convertible senior notes;
		Dilutive stock options;
		Unvested restricted stock units; and
		Employee Stock Purchase Plan, or ESPP.
Consolidation of variable interest entities
We identify entities as variable interest entities either: (1) that do not have sufficient equity investment at risk to permit the entity to finance its activities without additional subordinated financial support, or (2) in which the equity investors lack an essential characteristic of a controlling financial interest. We perform ongoing qualitative assessments of our variable interest entities to determine whether we have a controlling financial interest in the variable interest entity and therefore are the primary beneficiary. As of March 31, 2015 and December 31, 2014, we had collaborative arrangements with two entities, Regulus and Antisense Therapeutics Limited, that we considered to be variable interest entities. We are not the primary beneficiary for any of these entities as we do not have the power to direct the activities that most significantly impact the economic performance of our variable interest entities, the obligation to absorb losses, or the right to receive benefits from our variable interest entities that could potentially be significant to the variable interest entities. As of March 31, 2015, the total carrying value of our investments in variable interest entities was $93.4 million, and was related to our investment in Regulus. Our maximum exposure to loss related to our variable interest entities is limited to the carrying value of our investments.
Accumulated other comprehensive income
Accumulated other comprehensive income is comprised of unrealized gains and losses on investments, net of taxes, and adjustments we made to reclassify realized gains and losses on investments from other accumulated comprehensive income to our condensed consolidated statement of operations. The following table summarizes changes in accumulated other comprehensive income for the three months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended
		March 31,
		2015				2014
Beginning balance accumulated other comprehensive income		$	39,747			$	21,080
Other comprehensive income before reclassifications, net of tax (1)			7,367				8,261
Amounts reclassified from accumulated other comprehensive income (2)			—				(341	)
Net current period other comprehensive income			7,367				7,920
Ending balance accumulated other comprehensive income		$	47,114			$	29,000
	-1	Other comprehensive income from the three months ended March 31, 2015 includes income tax expense of $5.1 million, compared to $5.4 million for the three months ended March 31, 2014.
	-2	Included in gain on investments, net on our condensed consolidated statement of operations.
Convertible debt
We account for convertible debt instruments, including our 1 percent and 2¾ percent convertible notes, that may be settled in cash upon conversion (including partial cash settlement) by separating the liability and equity components of the instruments in a manner that reflects our nonconvertible debt borrowing rate. We determine the carrying amount of the liability component by measuring the fair value of similar debt instruments that do not have the conversion feature. If no similar debt instrument exists, we estimate fair value by using assumptions that market participants would use in pricing a debt instrument, including market interest rates, credit standing, yield curves and volatilities. Determining the fair value of the debt component requires the use of accounting estimates and assumptions. These estimates and assumptions are judgmental in nature and could have a significant impact on the determination of the debt component, and the associated non-cash interest expense.
We assign a value to the debt component of our convertible notes equal to the estimated fair value of similar debt instruments without the conversion feature, which resulted in us recording our debt at a discount. We are amortizing the debt discount over the life of the convertible notes as additional non-cash interest expense utilizing the effective interest method.
Segment information
In 2015, we began operating as two segments, our Isis Core segment, previously referred to as Drug Discovery and Development, and our new segment, Akcea Therapeutics, which includes the operations of our newly-formed and wholly-owned subsidiary, Akcea Therapeutics, Inc. We formed Akcea to develop and commercialize the drugs from our lipid franchise. We provide segment financial information and results for our Isis Core segment and our Akcea Therapeutics segment based on the segregation of revenues and expenses that our chief decision maker reviews to assess operating performance and to make operating decisions. We use judgments and estimates in determining the allocation of shared expenses to the two segments. Different assumptions or allocation methods could result in materially different results by segment.
Stock-based compensation expense
We measure stock-based compensation expense for equity-classified awards, principally related to stock options, restricted stock units, or RSUs, and stock purchase rights under our ESPP, based on the estimated fair value of the award on the date of grant. We recognize the value of the portion of the award that we ultimately expect to vest as stock-based compensation expense over the requisite service period in our condensed consolidated statements of operations. We reduce stock-based compensation expense for estimated forfeitures at the time of grant and revise in subsequent periods if actual forfeitures differ from those estimates.
We use the Black-Scholes model to estimate the fair value of stock options granted and stock purchase rights under our ESPP. The expected term of stock options granted represents the period of time that we expect them to be outstanding. We estimate the expected term of options granted based on historical exercise patterns. For the three months ended March 31, 2015 and 2014, we used the following weighted-average assumptions in our Black-Scholes calculations:
Employee Stock Options:
	Three Months Ended
	March 31,
	2015			2014
Risk-free interest rate		1.50%			1.60%
Dividend yield		0.00%			0.00%
Volatility		53.50%			50.50%
Expected life		4.5 years			4.6 years
ESPP:
	Three Months Ended
	March 31,
	2015			2014
Risk-free interest rate		0.10%			0.10%
Dividend yield		0.00%			0.00%
Volatility		56.20%			59.00%
Expected life		6 months			6 months
Board of Director Stock Options:
		Three Months Ended
		31-Mar-14
Risk-free interest rate			2.3	%
Dividend yield			0	%
Volatility			53.3	%
Expected life		7.1 years
The fair value of RSUs is based on the market price of our common stock on the date of grant. RSUs vest annually over a four year period. The weighted-average grant date fair value of RSUs granted to employees for the three months ended March 31, 2015 was $68.84 per share.
We did not grant any stock options or RSUs to the Board of Directors for the three months ended March 31, 2015.
The following table summarizes stock-based compensation expense for the three months ended March 31, 2015 and 2014 (in thousands), which was allocated as follows:
	Three Months Ended
	March 31,
	2015				2014
Research, development and patent expenses		$	10,486			$	5,873
General and administrative			2,819				1,196
Total		$	13,305			$	7,069
Non-cash stock-based compensation expense was $13.3 million for the three months ended March 31, 2015, and increased compared to $7.1 million for the same period in 2014 primarily due to the increase in our stock price. As of March 31, 2015, total unrecognized estimated non-cash stock-based compensation expense related to non-vested stock options and RSUs was $60.2 million and $25.0 million, respectively. We will adjust total unrecognized compensation cost for future changes in estimated forfeitures. We expect to recognize the cost of non-cash, stock-based compensation expense related to non-vested stock options and RSUs over a weighted average amortization period of 1.5 years and 1.8 years, respectively.
Impact of recently issued accounting standards
In May 2014, the FASB issued accounting guidance on the recognition of revenue from customers. Under this guidance, an entity will recognize revenue when it transfers promised goods or services to customers in an amount that reflects what the entity expects in exchange for the goods or services. This guidance also requires more detailed disclosures to enable users of the financial statements to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The guidance as currently issued is effective for fiscal years, and interim periods within that year, beginning after December 15, 2016 and will be effective for us in our fiscal year beginning January 1, 2017. On April 1, 2015, the FASB voted to propose deferring the effective date by one year. The FASB would still permit entities to choose to adopt on the original effective date. The proposal is subject to the FASB’s due process requirement, which includes a period for public comment. The guidance allows us to select one of two methods of adoption, either the full retrospective approach, meaning the guidance would be applied to all periods presented, or modified retrospective, meaning the cumulative effect of applying the guidance would be recognized as an adjustment to our opening retained earnings balance. We are currently in the process of determining the adoption method and timing as well as the effects the adoption will have on our consolidated financial statements and disclosures.
In August 2014, the FASB issued accounting guidance on how and when to disclose going-concern uncertainties in the financial statements. This guidance will require us to perform interim and annual assessments to determine our ability to continue as a going concern within one year from the date that we issue our financial statements. The guidance is effective for fiscal years, and interim periods within that year, beginning after December 15, 2016. We will adopt this guidance in our fiscal year beginning January 1, 2017. We do not expect this guidance to have any effect on our financial statements.
In February 2015, the FASB issued accounting guidance which amends existing consolidation guidance for entities that are required to evaluate whether they should consolidate certain legal entities. The guidance is effective for fiscal years, and interim periods within that year, beginning after December 15, 2015. We will adopt this guidance in our fiscal year beginning January 1, 2016. We do not expect this guidance to have any effect on our financial statements.
In April 2015, the FASB issued accounting guidance to simplify the presentation of debt issuance costs. The amended guidance requires us to present debt issuance costs as a direct deduction from the carrying amount of the related debt liability rather than as an asset. The guidance does not require us to change how we recognize and measure our debt issuance costs. The guidance is effective for fiscal years, and interim periods within that year, beginning after December 15, 2015. We will adopt this guidance in our fiscal year beginning January 1, 2016. We do not expect this guidance to have a material impact on our financial statements.
In April 2015, the FASB issued accounting guidance to clarify the accounting for fees paid in cloud computing arrangements. The amendment provides guidance to customers about whether a cloud computing arrangement includes a software license element consistent with the acquisition of other software licenses or if the arrangement excludes a software license and should be accounted for as a service contract. The guidance does not change the accounting for service contracts. The guidance is effective for fiscal years, and interim periods within that year, beginning after December 15, 2015. We can choose to adopt it either prospectively or retrospectively. We will adopt this guidance in our fiscal year beginning January 1, 2016. We are currently evaluating the impact, if any, of the adoption of this newly issued guidance to our condensed consolidated financial statements.

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Investments [Abstract]
Investments		3	Investments
	As of March 31, 2015, we have primarily invested our excess cash in debt instruments of the U.S. Treasury, financial institutions, corporations, and U.S. government agencies with strong credit ratings and an investment grade rating at or above A-1, P-1 or F-1 by Moody’s, Standard & Poor’s, or S&P, or Fitch, respectively. We have established guidelines relative to diversification and maturities that maintain safety and liquidity. We periodically review and modify these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity.
	The following table summarizes the contract maturity of the available-for-sale securities we held as of March 31, 2015:
	One year or less	58%
	After one year but within two years	29%
	After two years but within three years	13%
	Total	100%
	As illustrated above, at March 31, 2015, 87 percent of our available-for-sale securities had a maturity of less than two years.
	All of our available-for-sale securities are available to us for use in our current operations. As a result, we categorize all of these securities as current assets even though the stated maturity of some individual securities may be one year or more beyond the balance sheet date.
	At March 31, 2015, we had an ownership interest of less than 20 percent in one private company and two public companies with which we conduct business. The privately-held company is Atlantic Pharmaceuticals Limited and the publicly-traded companies are Antisense Therapeutics Limited and Regulus. We account for equity investments in the privately-held company under the cost method of accounting and we account for equity investments in the publicly-traded companies at fair value. We record unrealized gains and losses as a separate component of comprehensive income (loss) and include net realized gains and losses in gain (loss) on investments.
	The following is a summary of our investments (in thousands):
			Amortized			Gross Unrealized							Other-				Estimated
													Than-
													Temporary
													Impairment
	31-Mar-15		Cost			Gains			Losses				Loss				Fair Value
	Available-for-sale securities:
	Corporate debt securities		$	190,437		$	87		$	(31	)		$	—			$	190,493
	Debt securities issued by U.S. government agencies			53,006			5			(13	)			—				52,998
	Debt securities issued by the U.S. Treasury			5,999			4			—				—				6,003
	Debt securities issued by states of the United States and political subdivisions of the states (1)			46,571			25			(50	)			—				46,546
	Total securities with a maturity of one year or less			296,014			121			(94	)			—				296,040
	Corporate debt securities			137,653			124			(162	)			—				137,615
	Debt securities issued by U.S. government agencies			62,529			29			(14	)			—				62,544
	Debt securities issued by states of the United States and political subdivisions of the states			59,667			48			(165	)			—				59,550
	Total securities with a maturity of more than one year			259,849			201			(341	)			—				259,709
	Total available-for-sale securities		$	555,862		$	322		$	(435	)		$	—			$	555,749
		Cost			Gross Unrealized							Other-				Estimated
												Than-
												Temporary
												Impairment
	31-Mar-15	Basis			Gains			Losses				Loss				Fair Value
	Equity securities:
	Regulus Therapeutics Inc.		$	12,477		$	80,969		$	—			$	—			$	93,446
	Securities included in other current assets			880			—			—				(880	)			—
	Total equity securities		$	13,357		$	80,969		$	—			$	(880	)		$	93,446
	Total available-for-sale and equity securities		$	569,220		$	81,291		$	(435	)		$	(880	)		$	649,195
			Amortized			Gross Unrealized							Other-				Estimated
													Than-
													Temporary
													Impairment
	31-Dec-14		Cost			Gains			Losses				Loss				Fair Value
	Available-for-sale securities:
	Corporate debt securities(1)		$	219,856		$	89		$	(89	)		$	—			$	219,856
	Debt securities issued by U.S. government agencies			47,496			7			(27	)			—				47,476
	Debt securities issued by the U.S. Treasury (1)			19,008			9			—				—				19,017
	Debt securities issued by states of the United States and political subdivisions of the states (1)			45,196			19			(53	)			—				45,162
	Total securities with a maturity of one year or less			331,556			124			(169	)			—				331,511
	Corporate debt securities			152,730			16			(600	)			—				152,146
	Debt securities issued by U.S. government agencies			62,530			—			(151	)			—				62,379
	Debt securities issued by states of the United States and political subdivisions of the states			60,073			32			(234	)			—				59,871
	Total securities with a maturity of more than one year			275,333			48			(985	)			—				274,396
	Total available-for-sale securities		$	606,889		$	172		$	(1,154	)		$	—			$	605,907
		Cost			Gross Unrealized							Other-				Estimated
												Than-
												Temporary
												Impairment
	31-Dec-14	Basis			Gains			Losses				Loss				Fair Value
	Equity securities:
	Regulus Therapeutics Inc.		$	12,477		$	69,404		$	—			$	—			$	81,881
	Securities included in other current assets			880			—			—				(880	)			—
	Total equity securities		$	13,357		$	69,404		$	—			$	(880	)		$	81,881
	Total available-for-sale and equity securities		$	620,246		$	69,576		$	(1,154	)		$	(880	)		$	687,788
		-1	Includes investments classified as cash equivalents on our condensed consolidated balance sheet.
Investments we considered to be temporarily impaired at March 31, 2015 were as follows (in thousands):
					Less than 12 months of							More than 12 months of							Total temporary
					temporary impairment							temporary impairment							impairment
		Number of			Estimated			Unrealized				Estimated				Unrealized			Estimated		Unrealized
		Investments			Fair Value			Losses				Fair Value				Losses			Fair Value		Losses
Corporate debt securities			132		$	136,603		$	(193	)		$	—			$	—		$	136,603	$	(193	)
Debt securities issued by U.S. government agencies			11			74,094			(27	)			—				—			74,094		(27	)
Debt securities issued by states of the United States and political subdivisions of the states			24			42,943			(144	)			6,231				(71	)		49,174		(215	)
Total temporarily impaired securities			167		$	253,640		$	(364	)		$	6,231			$	(71	)	$	259,871	$	(435	)
We believe that the decline in value of these securities is temporary and primarily related to the change in market interest rates since purchase. We believe it is more likely than not that we will be able to hold these securities to maturity. Therefore we anticipate full recovery of their amortized cost basis at maturity.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Measurements [Abstract]
Fair Value Measurements		4	Fair Value Measurements
	We use a three-tier fair value hierarchy to prioritize the inputs used in our fair value measurements. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets for identical assets, which includes our money market funds and treasury securities classified as available-for-sale securities and our investment in equity securities in publicly-held biotechnology companies; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable, which includes our fixed income securities and commercial paper classified as available-for-sale securities; and Level 3, defined as unobservable inputs in which little or no market data exists, therefore requiring us to develop our own assumptions. Our Level 3 investments include our investments in the equity securities of publicly-held biotechnology companies for which we calculated a lack of marketability discount because there were restrictions on when we could trade the securities. We determine the lack of marketability discount by using a Black-Scholes model to value a hypothetical put option to approximate the cost of hedging the stock until the restriction ends. The majority of our securities have been classified as Level 2. We obtain the fair value of our Level 2 investments from our custodian bank or from a professional pricing service. We validate the fair value of our Level 2 investments by understanding the pricing model used by the custodian banks or professional pricing service provider and comparing that fair value to the fair value based on observable market prices. During the three months ended March 31, 2015, there were no transfers between our Level 1 and Level 2 investments. We recognize transfers between levels of the fair value hierarchy on the date of the event or change in circumstances that caused the transfer.
	We measure the following major security types at fair value on a recurring basis. The following summary breaks down the fair-value hierarchy that we used to value each security at March 31, 2015 and December 31, 2014 (in thousands):
			At			Quoted Prices in		Significant Other		Significant
			March 31,			Active Markets		Observable		Unobservable
			2015			(Level 1)		Inputs		Inputs
								(Level 2)		(Level 3)
	Cash equivalents (1)		$	112,777		$	112,777	$	—	$	—
	Corporate debt securities (2)			328,108			—		328,108		—
	Debt securities issued by U.S. government agencies (2)			115,542			—		115,542		—
	Debt securities issued by the U.S. Treasury (2)			6,003			6,003		—		—
	Debt securities issued by states of the United States and political subdivisions of the states (3)			106,096			—		106,096		—
	Investment in Regulus Therapeutics Inc.			93,446			93,446		—		—
	Total		$	761,972		$	212,226	$	549,746	$	—
			At			Quoted Prices in		Significant Other		Significant
			December 31,			Active Markets		Observable		Unobservable
			2014			(Level 1)		Inputs		Inputs
								(Level 2)		(Level 3)
	Cash equivalents (1)		$	104,680		$	104,680	$	—	$	—
	Corporate debt securities (4)			372,002			—		372,002		—
	Debt securities issued by U.S. government agencies (2)			109,855			—		109,855		—
	Debt securities issued by the U.S. Treasury (5)			19,017			19,017		—		—
	Debt securities issued by states of the United States and political subdivisions of the states (6)			105,033			—		105,033		—
	Investment in Regulus Therapeutics Inc.			81,881			—		—		81,881
	Total		$	792,468		$	123,697	$	586,890	$	81,881
		-1	Included in cash and cash equivalents on our condensed consolidated balance sheet.
		-2	Included in short-term investments on our condensed consolidated balance sheet.
		-3	$9.0 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
		-4	$0.8 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
		-5	$10 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
		-6	$9.3 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
	In November 2014, Regulus completed a public offering. As part of the offering, we sold shares of Regulus' common stock and became subject to trading restrictions on our remaining shares through January 2015. Therefore, at December 31, 2014, our investment in Regulus included a lack of marketability discount and was classified as a Level 3 investment. At the end of January 2015, we reclassified our investment in Regulus to a Level 1 investment because the contractual trading restrictions on the shares we own ended.
	The following is a summary of our investments measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the three months ended March 31, 2015 (in thousands):
	Beginning balance of Level 3 investments		$	81,881
	Total gain included in accumulated other comprehensive income (loss)			22,377
	Transfers out of Level 3 investments			(104,258	)
	Ending balance of Level 3 investments		$	—
	Other Fair Value Disclosures
	Our 1 percent and 2¾ percent convertible notes had a fair value of $233.7 million and $584.7 million, respectively at March 31, 2015. We determine the fair value of our convertible notes based on quoted market prices for these notes, which are Level 2 measurements.

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2015
Income Taxes [Abstract]
Income Taxes		5	Income Taxes
	Intraperiod tax allocation rules require us to allocate our provision for income taxes between continuing operations and other categories of earnings, such as other comprehensive income. In periods in which we have a year-to-date pre-tax loss from continuing operations and pre-tax income in other categories of earnings, such as other comprehensive income, we must allocate the tax provision to the other categories of earnings. We then record a related tax benefit in continuing operations. During the three months ended March 31, 2015 and 2014, we recorded unrealized gains on our investments in available-for-sale securities in other comprehensive income, net of taxes. As a result, for the three months ended March 31, 2015 and 2014, we recorded a $0.8 million and $2.3 million tax benefit, respectively, on our condensed consolidated statements of operations and a $5.1 million and $5.4 million tax expense, respectively, in other comprehensive income.

Collaborative_Arrangements_and

Collaborative Arrangements and Licensing Agreements	3 Months Ended
	Mar. 31, 2015
Collaborative Arrangements and Licensing Agreements [Abstract]
Collaborative Arrangements and Licensing Agreements		6	Collaborative Arrangements and Licensing Agreements
	Traditional Pharmaceutical Alliances and Licensing
	Bayer HealthCare
	In May 2015, we entered into an exclusive license agreement with Bayer HealthCare to develop and commercialize ISIS-FXIRx for the prevention of thrombosis. We are responsible for completing ongoing development activities. Bayer HealthCare is responsible for all other development and commercialization activities for ISIS-FXIRx. This transaction is subject to clearances under the Hart-Scott Rodino Antitrust Improvements Act.
	Under the terms of the agreement, we are eligible to receive $155 million in near-term payments, including an immediate $100 million payment and a $55 million milestone payment upon advancement of the program following a Phase 2 study in patients with compromised kidney function. Over the term of the agreement, we are eligible to receive up to $375 million in license fees, milestone payments and other payments, including up to $120 million for the achievement of development milestones and up to $110 million for the achievement of commercialization milestones. In addition, we are eligible to receive tiered royalties in the low to high 20 percent range on gross margins of ISIS-FXIRx. We will earn the next milestone payment of $55 million upon the advancement of the program following a Phase 2 study of ISIS-FXIRx in patients with compromised kidney function.
	Our agreement with Bayer HealthCare will continue until the expiration of all payment obligations under the agreement. In addition, the agreement, or any program under the agreement, may terminate early under the following situations:
			Bayer HealthCare may terminate the agreement or any program at any time by providing written notice to us;
			Either we or Bayer HealthCare may terminate the agreement or any program by providing written notice to the other party upon the other party’s uncured failure to perform a material obligation under the agreement, or the entire agreement if the other party becomes insolvent; and
			If Hart-Scott Rodino clearance is not received by December 31, 2015.
	Biogen
	We have established four strategic collaborations with Biogen that broaden and expand our severe and rare disease franchise for neurological disorders.
	ISIS-SMNRx
	In January 2012, we entered into a collaboration agreement with Biogen to develop and commercialize ISIS-SMNRx for the treatment of SMA. We are currently conducting a Phase 3 study evaluating ISIS-SMNRx in infants with SMA and a Phase 3 study evaluating ISIS-SMNRx in children with SMA. In addition, we are evaluating ISIS-SMNRx in two Phase 2 open-label, multiple-dose, dose-escalation studies, one in children with SMA and one in infants with SMA. Patients from both of the Phase 2 studies continue to have access to ISIS-SMNRx through open-label extension dosing. We are responsible for completing the Phase 2 and Phase 3 trials we are currently conducting. If Biogen exercises its option, it will pay us a license fee and will assume all other global development, regulatory and commercialization responsibilities. Biogen has the option to license ISIS-SMNRx. Biogen may exercise this option upon completion of and data review of the first successful Phase 2/3 trial or completion of both Phase 2/3 trials. An amendment in December 2014 provided for additional opt-in scenarios, based on the filing or the acceptance of a new drug application or marketing authorization application with the FDA or EMA.
	We received an upfront payment of $29 million, which we are amortizing through February 2017. We are also eligible to receive a license fee, milestone payments and royalties up to the mid-teens on any product sales of ISIS-SMNRx. In 2014, we and Biogen amended our original agreement to reflect changes made to the clinical development plan for ISIS-SMNRx. As a result, we and Biogen agreed to increase the payments that we are eligible to receive under this collaboration by approximately $57 million. Under the terms of the amended agreement, we are eligible to receive up to $327 million in a license fee and payments, including $102 million in substantive milestone and other payments associated with the clinical development of ISIS-SMNRx prior to licensing and $150 million in substantive milestone payments if Biogen achieves pre-specified regulatory milestones. In the first quarter of 2015, we earned a $9 million milestone payment for advancing the Phase 3 study of ISIS-SMNRx in infants with SMA and we earned a $7 million milestone payment for advancing the open-label extension study of ISIS-SMNRx in children with SMA. From inception through March 2015, we have received nearly $110 million in payments for advancing ISIS-SMNRx. We will earn the next milestone payment of $8.5 million if we further advance the Phase 3 study in infants with SMA.
	ISIS-DMPK-2.5Rx
	In June 2012, we and Biogen entered into a second and separate collaboration agreement to develop and commercialize a novel antisense drug, ISIS-DMPK-2.5Rx, targeting DMPK for the treatment of myotonic dystrophy type 1, or DM1. We are responsible for global development of the drug through the completion of the first Phase 2 clinical trial. Biogen has the option to license the drug through the completion of the first Phase 2 trial. If Biogen exercises its option, it will assume all other global development, regulatory and commercialization responsibilities. Under the terms of the agreement, we received an upfront payment of $12 million, which we are amortizing through June 2017. Over the term of the collaboration, we are eligible to receive up to $259 million in a license fee and substantive milestone payments, including up to $59 million in development milestone payments and $130 million in milestone payments if Biogen achieves pre-specified regulatory milestones. In addition, we are eligible to receive royalties up to the mid-teens on any product sales of the drug. From inception through March 2015, we have received $36 million in payments for advancing ISIS-DMPK-2.5Rx. We will earn the next milestone payment of $35 million if we initiate a Phase 2 study for ISIS-DMPK-2.5Rx.
	Neurology
	In December 2012, we and Biogen entered into a third and separate collaboration agreement to develop and commercialize novel antisense drugs to three targets to treat neurological or neuromuscular diseases. We are responsible for the development of each of the drugs through the completion of the initial Phase 2 clinical study for such drug. Biogen has the option to license a drug from each of the three programs through the completion of the first Phase 2 study for each program. If Biogen exercises its option for a drug, it will assume all further global development, regulatory and commercialization responsibilities for that drug. Under the terms of the agreement, we received an upfront payment of $30 million, which we are amortizing through December 2020. Over the term of the collaboration, we are eligible to receive up to $259 million in a license fee and substantive milestone payments per program. We are eligible to receive up to $59 million in development milestone payments to support research and development of each program, including amounts related to the cost of clinical trials. We are also eligible to receive up to $130 million in milestone payments per program if Biogen achieves pre-specified regulatory milestones. In addition, we are eligible to receive royalties up to the mid-teens on any product sales of drugs resulting from each of the three programs. In February 2015, we earned a $10 million milestone payment when we initiated an IND-enabling toxicology study of ISIS-BIIB4Rx, a drug for an undisclosed target designed to treat a neurodegenerative disease. From inception through March 31, 2015, we have received $40 million in payments under this collaboration. We will earn the next milestone payment of up to $14 million if we initiate a Phase 1 study for ISIS-BIIB4Rx.
	Strategic Neurology
	In September 2013, we and Biogen entered into a fourth and separate collaboration agreement, which is a long-term strategic relationship focused on applying antisense technology to advance the treatment of neurological diseases. As part of the collaboration, Biogen gained exclusive rights to the use of our antisense technology to develop therapies for neurological diseases and has the option to license drugs resulting from this collaboration. The exclusivity for neurological diseases will last through September 2019, and may be extended for any drug development programs being pursued under the collaboration. We will usually be responsible for drug discovery and early development of antisense drugs and Biogen will have the option to license antisense drugs after Phase 2 proof of concept. If Biogen exercises its option for a drug, it will assume all further global development, regulatory and commercialization responsibilities for that drug. Biogen will be responsible for all of the drug discovery and development activities for drugs using other modalities.
	Under the terms of the agreement, we received an upfront payment of $100 million and are eligible to receive milestone payments, license fees and royalty payments for all drugs developed through this collaboration, with the specific amounts dependent upon the modality of the molecule advanced by Biogen. If we have a change of control during the first six years of the collaboration, we may be required to refund Biogen a portion of the $100 million upfront payment, with the amount of the potential refund decreasing ratably as we progress through the initial six year term of the collaboration. We are amortizing the $100 million upfront payment through September 2019. Because the amortization period for the upfront payment will never be less than the initial six year term of the collaboration, the amount of revenue we recognize from the upfront payment will never exceed the amount that Biogen could potentially require us to refund.
	For each antisense molecule that is chosen for drug discovery and development under this collaboration, we are eligible to receive up to approximately $260 million in a license fee and substantive milestone payments. We are eligible to receive up to approximately $60 million for the achievement of research and development milestones, including amounts related to the cost of clinical trials, and up to $130 million for the achievement of regulatory milestones. In addition, we are eligible to receive royalties up to the mid-teens on any product sales of antisense drugs developed under this collaboration. If other modalities are chosen, such as small molecules or monoclonal antibodies, we are eligible to receive up to $90 million in substantive milestone payments, including up to $35 million for the achievement of research and development milestones and up to $55 million for the achievement of regulatory milestones. In addition, we are eligible to receive single-digit royalties on any product sales of drugs using non-antisense modalities developed under this collaboration. From inception through March 2015, we have received $125 million in payments under this collaboration. In April 2015, we earned a $10 million milestone payment for validating a fourth target under this collaboration. We will earn the next milestone payment of up to $10 million if we choose another target to advance under this collaboration.
	Each of our agreements with Biogen will continue until the earlier of the date all of Biogen's options to obtain the exclusive licenses under the applicable agreement expire unexercised or, if Biogen exercises its option, until the expiration of all payment obligations under the applicable agreement. In addition, each agreement, or any program under an agreement, may terminate early under the following situations:
			Biogen may terminate the agreement or any program at any time by providing written notice to us;
			Under specific circumstances, if we are acquired by a third party with a product that directly competes with a compound being developed under the agreement, Biogen may terminate the affected program by providing written notice to us;
			If, within a specified period of time, any required clearance of a transaction contemplated by an agreement under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, is not received, then either we or Biogen may terminate the affected program by providing written notice to the other party; and
			Either we or Biogen may terminate any program by providing written notice to the other party upon the other party's uncured failure to perform a material obligation under the agreement with respect to the affected program, or the entire agreement if the other party becomes insolvent.
	During the three months ended March 31, 2015 and 2014, we earned revenue of $39.2 million and $10.2 million, respectively, from our relationship with Biogen, which represented 63 and 36 percent, respectively of our total revenue for those periods. Our condensed consolidated balance sheet at March 31, 2015 included deferred revenue of $110.8 million related to our relationship with Biogen.
	GSK
	In March 2010, we entered into a strategic alliance with GSK using our antisense drug discovery platform to seek out and develop new drugs against targets for rare and serious diseases, including infectious diseases and some conditions causing blindness. Our strategic alliance currently includes five drugs in development. GSK has the exclusive option to license drugs resulting from this alliance at Phase 2 proof-of-concept for a license fee. If GSK exercises its exclusive option for any drugs resulting from this alliance, it will be responsible for all further global development, regulatory and commercialization activities for such drug. Under the terms of the agreement, we received a $35 million upfront payment and in May 2011 we received a $3 million payment when we and GSK expanded the collaboration.
	In October 2012, we and GSK amended the original agreement to reflect an accelerated clinical development plan for ISIS-TTRRx. From inception through March 2015, we have earned $60 million, primarily in milestone payments, from GSK related to the development of ISIS-TTRRx. We are also eligible to earn an additional $10 million pre-licensing milestone payment associated with the ISIS-TTRRx Phase 2/3 study. In addition, under the amended agreement, we and GSK increased the regulatory and commercial milestone payments we can earn should ISIS-TTRRx receive marketing approval and meet pre-agreed sales targets.
	In addition to ISIS-TTRRx, we have four drugs in development. We are developing ISIS-HBVRx, an antisense drug designed to reduce the production of viral proteins associated with hepatitis B virus, or HBV infection. We are also developing ISIS-GSK4-LRx and ISIS-RHO-2.5Rx, which are antisense drugs we designed to treat ocular diseases. In addition, we recently advanced a drug to treat an undisclosed target, ISIS-GSK6-LRx, into development.
	Under our agreement, if GSK successfully develops all five drugs for one or more indications and achieves pre-agreed sales targets, we could receive license fees and substantive milestone payments of more than $1.3 billion, including up to $220.5 million for the achievement of development milestones, up to $483.5 million for the achievement of regulatory milestones and up to $428 million for the achievement of commercialization milestones. Through March 2015, we have received $129.5 million in payments under this strategic alliance with GSK. We will earn the next milestone payment of $5 million if we further advance ISIS-GSK4Rx. In addition, we are eligible to receive royalties up to the mid-teens on sales from any product that GSK successfully commercializes under this alliance.
	Our alliance with GSK will continue until the earlier of the date that all of GSK's options to obtain the exclusive licenses under the agreement expire unexercised or, if GSK exercises its option, until the expiration of all payment obligations under the agreement. In addition, the agreement, or any program under the agreement, may terminate early under the following situations:
			GSK may terminate any program, other than the ISIS-TTRRx program, at any time by providing written notice to us;
			GSK may terminate the ISIS-TTRRx program by providing written notice to us after reviewing specific data from the Phase 3 study for the program; and
			Either we or GSK may terminate any program by providing written notice to the other party upon the other party's uncured failure to perform a material obligation under the agreement with respect to the affected program, or the entire agreement if the other party becomes insolvent.
	During the three months ended March 31, 2015 and 2014, we earned revenue of $16.5 million and $3.3 million, respectively, from our relationship with GSK, which represented 26 and 12 percent, respectively of our total revenue for those periods. Our condensed consolidated balance sheet at March 31, 2015 included deferred revenue of $9.2 million related to our relationship with GSK.

Segment_Information_and_Concen

Segment Information and Concentration of Business Risk	3 Months Ended
	Mar. 31, 2015
Segment Information and Concentration of Business Risk [Abstract]
Segment Information and Concentration of Business Risk		7	Segment Information and Concentration of Business Risk
	In 2015, we began reporting our financial results in two reportable segments, Isis Core, previously referred to as Drug Discovery and Development and Akcea Therapeutics, our new wholly owned subsidiary. Segment loss from operations includes revenue less operating expenses attributable to each segment.
	In our Isis Core segment we are exploiting a novel drug discovery platform we created to generate a broad pipeline of first-in-class or best-in-class drugs for us and our partners. Our Isis Core segment generates revenue from a multifaceted partnering strategy.
	We established Akcea to develop and commercialize the drugs from our lipid franchise. Moving our lipid drugs into a company that we own and control ensures that our core focus at Isis remains on innovation while allowing us to maintain control over and retain more value from our lipid drugs. To date, Akcea has not earned any revenue.
	The following is our segment information for the three months ended March 31, 2015 (in thousands).
		Isis Core				Akcea Therapeutics				Total
	Revenue:
	Research and development		$	61,892			$	—			$	61,892
	Licensing and royalty			691				—				691
	Total segment revenue		$	62,583			$	—			$	62,583
	Loss from operations		$	(2,232	)		$	(7,098	)		$	(9,330	)
	We have historically funded our operations from collaborations with corporate partners and a relatively small number of partners have accounted for a significant percentage of our revenue. Revenue from significant partners, which is defined as ten percent or more of our total revenue, was as follows:
		Three Months Ended
		March 31,
		2015			2014
	Partner A		63%			36%
	Partner B		26%			12%
	Partner C		1%			12%
	Partner D		0%			27%
	Contract receivables from two significant partners comprised approximately 92 percent of our contract receivables at March 31, 2015. Contract receivables from three significant partners comprised approximately 99 percent of our contract receivables at December 31, 2014.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Significant Accounting Policies [Abstract]
Revenue Recognition	Revenue Recognition
	We generally recognize revenue when we have satisfied all contractual obligations and are reasonably assured of collecting the resulting receivable. We are often entitled to bill our customers and receive payment from our customers in advance of recognizing the revenue. In the instances in which we have received payment from our customers in advance of recognizing revenue, we include the amounts in deferred revenue on our consolidated balance sheet.
	Arrangements with multiple deliverables
	Our collaboration agreements typically contain multiple elements, or deliverables, including technology licenses or options to obtain technology licenses, research and development services, and in certain cases manufacturing services, and we allocate the consideration to each unit of accounting based on the relative selling price of each deliverable.
	Identifying deliverables and units of accounting
	We evaluate the deliverables in our collaboration agreements to determine whether they meet the criteria to be accounted for as separate units of accounting or whether they should be combined with other deliverables and accounted for as a single unit of accounting. When the delivered items in an arrangement have "stand-alone value" to our customer, we account for the deliverables as separate units of accounting. For example, in December 2012, we entered into a global collaboration agreement with AstraZeneca to discover and develop antisense drugs against five cancer targets. As part of the collaboration, we received a $25 million upfront payment in December 2012 and a $6 million payment in June 2013 when AstraZeneca elected to continue the research collaboration. We are also eligible to receive milestone payments, license fees for the research program targets and royalties on any product sales of drugs resulting from this collaboration. In exchange, we granted AstraZeneca an exclusive license to develop and commercialize ISIS-STAT3-2.5Rx and ISIS-AR-2.5Rx. We also granted AstraZeneca options to license up to three cancer drugs under the separate research program. We were responsible for completing IND-enabling studies for ISIS-AR-2.5Rx, which we completed in early 2014. We were also responsible for completing an ongoing clinical study of ISIS-STAT3-2.5Rx, which we substantially completed in the first quarter of 2015. AstraZeneca is responsible for all other global development, regulatory and commercialization activities for ISIS-STAT3-2.5Rx and ISIS-AR-2.5Rx. In addition, if AstraZeneca exercises its option for any drugs resulting from the research program, AstraZeneca will assume global development, regulatory and commercialization responsibilities for such drug. Since this agreement has multiple elements, we evaluated the deliverables in this arrangement when we entered into the agreement and determined that certain deliverables, either individually or in combination, have stand-alone value. Below is a list of the four separate units of accounting under our agreement:
			The exclusive license we granted to AstraZeneca to develop and commercialize ISIS-STAT3-2.5Rx for the treatment of cancer;
			The development services we agreed to perform for ISIS-STAT3-2.5Rx;
			The exclusive license we granted to AstraZeneca to develop and commercialize ISIS-AR-2.5Rx and the research services we performed for ISIS-AR-2.5Rx; and
			The option to license up to three drugs under a research program and the research services we are performing for this program.
	Measurement and allocation of arrangement consideration
	Our collaborations may provide for various types of payments to us including upfront payments, funding of research and development, milestone payments, licensing fees, profit sharing and royalties on product sales. We initially allocate the amount of consideration that is fixed and determinable at the time the agreement is entered into and exclude contingent consideration. We allocate the consideration to each unit of accounting based on the relative selling price of each deliverable. Delivered items have stand-alone value if they are sold separately by any vendor or the customer could resell the delivered items on a stand-alone basis. We use the following hierarchy of values to estimate the selling price of each deliverable: (i) vendor-specific objective evidence of fair value; (ii) third-party evidence of selling price; and (iii) best estimate of selling price, or BESP. The BESP reflects our best estimate of what the selling price would be if we regularly sold the deliverable on a stand-alone basis. We recognize the revenue allocated to each unit of accounting as we deliver the related goods or services. If we determine that we should treat certain deliverables as a single unit of accounting, then we recognize the revenue ratably over our estimated period of performance.
	We determined that the ISIS-STAT3-2.5Rx license had stand-alone value because it is an exclusive license that gives AstraZeneca the right to develop ISIS-STAT3-2.5Rx or to sublicense its rights. In addition, ISIS-STAT3-2.5Rx is currently in development and it is possible that AstraZeneca or another third party could conduct clinical trials without assistance from us. As a result, we considered the ISIS-STAT3-2.5Rx license and the development services for ISIS-STAT3-2.5Rx to be separate units of accounting. We recognized the portion of the consideration allocated to the ISIS-STAT3-2.5Rx license immediately because we delivered the license and earned the revenue. We recognized as revenue the amount allocated to the development services for ISIS-STAT3-2.5Rx over the period of time we performed services. The ISIS-AR-2.5Rx license is also an exclusive license. At the inception of the agreement, ISIS-AR-2.5Rx was in an early stage of research. Therefore, we concluded that our knowledge and expertise with antisense technology was essential for AstraZeneca or another third party to successfully develop ISIS-AR-2.5Rx. As a result, we determined that the ISIS-AR-2.5Rx license did not have stand-alone value and we combined the ISIS-AR-2.5Rx license and related research services into one unit of accounting. We recognized revenue for the combined unit of accounting over the period of time we performed services, which ended in the first quarter of 2014. We determined that the options under the research program did not have stand-alone value because AstraZeneca cannot develop or commercialize drugs resulting from the research program until AstraZeneca exercises the respective option or options. As a result, we considered the research options and the related research services as a combined unit of accounting. We are recognizing revenue for the combined unit of accounting over the period of our performance.
	We determined that the allocable arrangement consideration was $31 million and we allocated it based on the relative BESP of each unit of accounting. We engaged a third party, independent valuation expert to assist us with determining BESP. We estimated the selling price of the licenses granted for ISIS-STAT3-2.5Rx and ISIS-AR-2.5Rx by using the relief from royalty method. Under this method, we estimated the amount of income, net of taxes, for each drug. We then discounted the projected income for each license to present value. The significant inputs we used to determine the projected income of the licenses included:
			Estimated future product sales;
			Estimated royalties on future product sales;
			Contractual milestone payments;
			Expenses we expect to incur;
			Income taxes; and
			An appropriate discount rate.
	We estimated the selling price of the research and development services by using our internal estimates of the cost to perform the specific services, marked up to include a reasonable profit margin, and estimates of expected cash outflows to third parties for services and supplies over the expected period that we will perform research and development. The significant inputs we used to determine the selling price of the research and development services included:
			The number of internal hours we will spend performing these services;
			The estimated number and cost of studies we will perform;
			The estimated number and cost of studies that we will contract with third parties to perform; and
			The estimated cost of drug product we will use in the studies.
	Timing of revenue recognition
	We recognize revenue over the period of our performance for each deliverable when we determine that it is realized or realizable and earned. Typically, we must estimate our period of performance when the agreements we enter into do not clearly define such information. Our collaborative agreements typically include a research and/or development project plan outlining the activities the agreement requires each party to perform during the collaboration. We estimate the period of time over which we will complete the activities for which we are responsible and use that period of time as our period of performance for purposes of revenue recognition and recognize revenue ratably over such period. We have made estimates of our continuing obligations under numerous agreements and in certain instances the timing of satisfying these obligations may change as the development plans for our drugs progress. Accordingly, our estimates may change in the future. If our estimates and judgments change over the course of these agreements, it may affect the timing and amount of revenue that we recognize in future periods.
	Multiple agreements
	From time to time, we may enter into separate agreements at or near the same time with the same customer. We evaluate such agreements to determine whether they should be accounted for individually as distinct arrangements or whether the separate agreements are, in substance, a single multiple element arrangement. We evaluate whether the negotiations are conducted jointly as part of a single negotiation, whether the deliverables are interrelated or interdependent, whether fees in one arrangement are tied to performance in another arrangement, and whether elements in one arrangement are essential to another arrangement. Our evaluation involves significant judgment to determine whether a group of agreements might be so closely related that they are, in effect, part of a single arrangement. For example, since early 2012 we have entered into four collaboration agreements with Biogen:
			In January 2012, we entered into a collaboration agreement with Biogen to develop and commercialize ISIS-SMNRx for spinal muscular atrophy, or SMA. As part of the collaboration, we received a $29 million upfront payment and we are responsible for global development of ISIS-SMNRx through completion of Phase 2/3 clinical trials.
			In June 2012, we entered into a second and separate collaboration agreement with Biogen to develop and commercialize a novel antisense drug targeting DMPK, or dystrophia myotonica-protein kinase. As part of the collaboration, we received a $12 million upfront payment and we are responsible for global development of the drug through the completion of a Phase 2 clinical trial.
			In December 2012, we entered into a third and separate collaboration agreement with Biogen to discover and develop antisense drugs against three targets to treat neurological or neuromuscular disorders. As part of the collaboration, we received $30 million upfront payment and we are responsible for the discovery of a lead antisense drug for each of three targets.
			In September 2013, we entered into a fourth and separate collaboration agreement with Biogen to leverage antisense technology to advance the treatment of neurological diseases. We granted Biogen exclusive rights to the use of our antisense technology to develop therapies for neurological diseases as part of this broad collaboration. We received a $100 million upfront payment and we are responsible for discovery and early development through the completion of a Phase 2 clinical trial for each antisense drug identified during the six year term of this collaboration, while Biogen is responsible for the creation and development of small molecule treatments and biologics.
	All four of these collaboration agreements give Biogen the option to license one or more drugs resulting from the specific collaboration. If Biogen exercises an option, it will pay us a license fee and will assume future development, regulatory and commercialization responsibilities for the licensed drug. We are also eligible to receive milestone payments associated with the research and/or development of the drugs prior to licensing, milestone payments if Biogen achieves pre-specified regulatory milestones, and royalties on any product sales of drugs resulting from these collaborations.
	We evaluated all four of the Biogen agreements to determine whether we should account for them as separate agreements. We determined that we should account for the agreements separately because we conducted the negotiations independently of one another, each agreement focuses on different drugs, there are no interrelated or interdependent deliverables, there are no provisions in any of these agreements that are essential to the other agreement, and the payment terms and fees under each agreement are independent of each other. We also evaluated the deliverables in each of these agreements to determine whether they met the criteria to be accounted for as separate units of accounting or whether they should be combined with other deliverables and accounted for as a single unit of accounting. For all four of these agreements, we determined that the options did not have stand-alone value because Biogen cannot pursue the development or commercialization of the drugs resulting from these collaborations until it exercises the respective option or options. As such, for each agreement we considered the deliverables to be a single unit of accounting and we are recognizing the upfront payment for each of the agreements over the respective estimated period of our performance.
	Milestone payments
	Our collaborations often include contractual milestones, which typically relate to the achievement of pre-specified development, regulatory and commercialization events. These three categories of milestone events reflect the three stages of the life-cycle of our drugs, which we describe in more detail in the following paragraph.
	Prior to the first stage in the life-cycle of our drugs, we perform a significant amount of work using our proprietary antisense technology to design chemical compounds that interact with specific genes that are good targets for drug discovery. From these research efforts, we hope to identify a development candidate. The designation of a development candidate is the first stage in the life-cycle of our drugs. A development candidate is a chemical compound that has demonstrated the necessary safety and efficacy in preclinical animal studies to warrant further study in humans.
	During the first step of the development stage, we or our partners study our drugs in IND-enabling studies, which are animal studies intended to support an Investigational New Drug, or IND, application and/or the foreign equivalent. An approved IND allows us or our partners to study our development candidate in humans. If the regulatory agency approves the IND, we or our partners initiate Phase 1 clinical trials in which we typically enroll a small number of healthy volunteers to ensure the development candidate is safe for use in patients. If we or our partners determine that a development candidate is safe based on the Phase 1 data, we or our partners initiate Phase 2 studies that are generally larger scale studies in patients with the primary intent of determining the efficacy of the development candidate.
	The final step in the development stage is Phase 3 studies to gather the necessary safety and efficacy data to request marketing approval from the Food and Drug Administration, or FDA, and/or foreign equivalents. The Phase 3 studies typically involve large numbers of patients and can take up to several years to complete. If the data gathered during the trials demonstrates acceptable safety and efficacy results, we or our partner will submit an application to the FDA and/or its foreign equivalents for marketing approval. This stage of the drug’s life-cycle is the regulatory stage.
	If a drug achieves marketing approval, it moves into the commercialization stage, during which our partner will market and sell the drug to patients. Although our partner will ultimately be responsible for marketing and selling the partnered drug, our efforts to discover and develop a drug that is safe, effective and reliable contributes significantly to our partner’s ability to successfully sell the drug. The FDA and its foreign equivalents have the authority to impose significant restrictions on an approved drug through the product label and on advertising, promotional and distribution activities. Therefore, our efforts designing and executing the necessary animal and human studies are critical to obtaining claims in the product label from the regulatory agencies that would allow us or our partner to successfully commercialize our drug. Further, the patent protection afforded our drugs as a result of our initial patent applications and related prosecution activities in the United States and foreign jurisdictions are critical to our partner’s ability to sell our drugs without competition from generic drugs. The potential sales volume of an approved drug is dependent on several factors including the size of the patient population, market penetration of the drug, and the price charged for the drug.
	Generally, the milestone events contained in our partnership agreements coincide with the progression of our drugs from development, to regulatory approval and then to commercialization. The process of successfully discovering a new development candidate, having it approved and ultimately sold for a profit is highly uncertain. As such, the milestone payments we may earn from our partners involve a significant degree of risk to achieve. Therefore, as a drug progresses through the stages of its life-cycle, the value of the drug generally increases.
	Development milestones in our partnerships may include the following types of events:
			Designation of a development candidate. Following the designation of a development candidate, IND-enabling animal studies for a new development candidate generally take 12 to 18 months to complete;
			Initiation of a Phase 1 clinical trial. Generally, Phase 1 clinical trials take one to two years to complete;
			Initiation or completion of a Phase 2 clinical trial. Generally, Phase 2 clinical trials take one to three years to complete;
			Initiation or completion of a Phase 3 clinical trial. Generally, Phase 3 clinical trials take two to four years to complete.
	Regulatory milestones in our partnerships may include the following types of events:
			Filing of regulatory applications for marketing approval such as a New Drug Application, or NDA, in the United States or a Marketing Authorization Application, or MAA, in Europe. Generally, it takes six to twelve months to prepare and submit regulatory filings.
			Marketing approval in a major market, such as the United States, Europe or Japan. Generally it takes one to two years after an application is submitted to obtain approval from the applicable regulatory agency.
	Commercialization milestones in our partnerships may include the following types of events
			First commercial sale in a particular market, such as in the United States or Europe.
			Product sales in excess of a pre-specified threshold, such as annual sales exceeding $1 billion. The amount of time to achieve this type of milestone depends on several factors including but not limited to the dollar amount of the threshold, the pricing of the product and the pace at which customers begin using the product.
	We assess whether a substantive milestone exists at the inception of our agreements. When a substantive milestone is achieved, we recognize revenue related to the milestone payment immediately. For our existing licensing and collaboration agreements in which we are involved in the discovery and/or development of the related drug or provide the partner with access to new technologies we discover, we have determined that the majority of future development, regulatory and commercialization milestones are substantive. For example, we consider most of the milestones associated with our strategic alliance with Biogen substantive because we are using our antisense drug discovery platform to discover and develop new drugs against targets for neurological diseases. Alternatively, we consider milestones associated with our strategic alliance with Alnylam Pharmaceuticals, Inc. substantive because we provide Alnylam ongoing access to our technology to develop and commercialize RNA interference, or RNAi, therapeutics. In evaluating if a milestone is substantive we consider whether:
			Substantive uncertainty exists as to the achievement of the milestone event at the inception of the arrangement;
			The achievement of the milestone involves substantive effort and can only be achieved based in whole or in part on our performance or the occurrence of a specific outcome resulting from our performance;
			The amount of the milestone payment appears reasonable either in relation to the effort expended or to the enhancement of the value of the delivered items;
			There is no future performance required to earn the milestone; and
			The consideration is reasonable relative to all deliverables and payment terms in the arrangement.
	If any of these conditions are not met, we do not consider the milestone to be substantive and we defer recognition of the milestone payment and recognize it as revenue over our estimated period of performance, if any. Further information about our collaborative arrangements can be found in Note 6, Collaborative Arrangements and Licensing Agreements.
	Licensing and royalty revenue
	We often enter into agreements to license our proprietary patent rights on an exclusive or non-exclusive basis in exchange for license fees and/or royalties. We generally recognize as revenue immediately those licensing fees and royalties for which we have no significant future performance obligations and are reasonably assured of collecting the resulting receivable. For example, in the first quarter of 2014, we recognized $7.7 million in revenue from Alnylam related to its license of our technology to one of its partners because we had no performance obligations and collectability was reasonably assured.
Cash, cash equivalents and short-term investments	Cash, cash equivalents and short-term investments
	We consider all liquid investments with maturities of three months or less when we purchase them to be cash equivalents. Our short-term investments have initial maturities of greater than three months from date of purchase. We classify our short-term investments as “available-for-sale” and carry them at fair market value based upon prices for identical or similar items on the last day of the fiscal period. We record unrealized gains and losses as a separate component of comprehensive income (loss) and include net realized gains and losses in gain (loss) on investments. We use the specific identification method to determine the cost of securities sold.
	We have equity investments in privately- and publicly-held biotechnology companies that we have received as part of a technology license or collaboration agreement. At March 31, 2015 we held ownership interests of less than 20 percent in each of the respective companies.
	We account for our equity investments in publicly-held companies at fair value and record unrealized gains and losses related to temporary increases and decreases in the stock of these publicly-held companies as a separate component of comprehensive income (loss). We account for equity investments in privately-held companies under the cost method of accounting because we own less than 20 percent and do not have significant influence over their operations. We hold one cost method investment in Atlantic Pharmaceuticals Limited. Realization of our equity position in this company is uncertain. When realization of our investment is uncertain, we record a full valuation allowance. In determining if and when a decrease in market value below our cost in our equity positions is temporary or other-than-temporary, we examine historical trends in the stock price, the financial condition of the company, near term prospects of the company and our current need for cash. If we determine that a decline in value in either a public or private investment is other-than-temporary, we recognize an impairment loss in the period in which the other-than-temporary decline occurs.
Inventory valuation	Inventory valuation
	We capitalize the costs of raw materials that we purchase for use in producing our drugs because until we use these raw materials they have alternative future uses. We include in inventory raw material costs for drugs that we manufacture for our partners under contractual terms and that we use primarily in our clinical development activities and drug products. We can use each of our raw materials in multiple products and, as a result, each raw material has future economic value independent of the development status of any single drug. For example, if one of our drugs failed, we could use the raw materials for that drug to manufacture our other drugs. We expense these costs when we deliver the drugs to our partners, or as we provide these drugs for our own clinical trials. We reflect our inventory on the balance sheet at the lower of cost or market value under the first-in, first-out method. We review inventory periodically and reduce the carrying value of items we consider to be slow moving or obsolete to their estimated net realizable value. We consider several factors in estimating the net realizable value, including shelf life of raw materials, alternative uses for our drugs and clinical trial materials, and historical write-offs. We did not record any inventory write-offs for the three months ended March 31, 2015 and 2014. Total inventory, which consisted of raw materials, was $6.8 million and $6.3 million as of March 31, 2015 and December 31, 2014, respectively.
Research, development and patent expenses	Research, development and patent expenses
	Our research and development expenses include wages, benefits, facilities, supplies, external services, clinical trial and manufacturing costs and other expenses that are directly related to our research and development operations. We expense research and development costs as we incur them. When we make payments for research and development services prior to the services being rendered, we record those amounts as prepaid assets on our condensed consolidated balance sheet and we expense them as the services are provided.
	We capitalize costs consisting principally of outside legal costs and filing fees related to obtaining patents. We amortize patent costs over the useful life of the patent, beginning with the date the United States Patent and Trademark Office, or foreign equivalent, issues the patent. We review our capitalized patent costs regularly to ensure that they include costs for patents and patent applications that have future value. We evaluate patents and patent applications that we are not actively pursuing and write off any associated costs.
Long-lived assets	Long-lived assets
	We evaluate long-lived assets, which include property, plant and equipment, patent costs, and exclusive licenses acquired from third parties, for impairment on at least a quarterly basis and whenever events or changes in circumstances indicate that we may not be able to recover the carrying amount of such assets.
Use of estimates	Use of estimates
	The preparation of condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ from those estimates.
Basic and diluted net loss per share	Basic and diluted net loss per share
	We compute basic net loss per share by dividing the net loss by the weighted-average number of common shares outstanding during the period. As we incurred a net loss for the three months ended March 31, 2015 and 2014, we did not include dilutive common equivalent shares in the computation of diluted net loss per share because the effect would have been anti-dilutive. Common stock from the following would have had an anti-dilutive effect on net loss per share:
			1 percent convertible senior notes;
			2¾ percent convertible senior notes;
			Dilutive stock options;
			Unvested restricted stock units; and
			Employee Stock Purchase Plan, or ESPP.
Consolidation of variable interest entities	Consolidation of variable interest entities
	We identify entities as variable interest entities either: (1) that do not have sufficient equity investment at risk to permit the entity to finance its activities without additional subordinated financial support, or (2) in which the equity investors lack an essential characteristic of a controlling financial interest. We perform ongoing qualitative assessments of our variable interest entities to determine whether we have a controlling financial interest in the variable interest entity and therefore are the primary beneficiary. As of March 31, 2015 and December 31, 2014, we had collaborative arrangements with two entities, Regulus and Antisense Therapeutics Limited, that we considered to be variable interest entities. We are not the primary beneficiary for any of these entities as we do not have the power to direct the activities that most significantly impact the economic performance of our variable interest entities, the obligation to absorb losses, or the right to receive benefits from our variable interest entities that could potentially be significant to the variable interest entities. As of March 31, 2015, the total carrying value of our investments in variable interest entities was $93.4 million, and was related to our investment in Regulus. Our maximum exposure to loss related to our variable interest entities is limited to the carrying value of our investments.
Accumulated other comprehensive income	Accumulated other comprehensive income
	Accumulated other comprehensive income is comprised of unrealized gains and losses on investments, net of taxes, and adjustments we made to reclassify realized gains and losses on investments from other accumulated comprehensive income to our condensed consolidated statement of operations. The following table summarizes changes in accumulated other comprehensive income for the three months ended March 31, 2015 and 2014 (in thousands):
			Three Months Ended
			March 31,
			2015				2014
	Beginning balance accumulated other comprehensive income		$	39,747			$	21,080
	Other comprehensive income before reclassifications, net of tax (1)			7,367				8,261
	Amounts reclassified from accumulated other comprehensive income (2)			—				(341	)
	Net current period other comprehensive income			7,367				7,920
	Ending balance accumulated other comprehensive income		$	47,114			$	29,000
		-1	Other comprehensive income from the three months ended March 31, 2015 includes income tax expense of $5.1 million, compared to $5.4 million for the three months ended March 31, 2014.
		-2	Included in gain on investments, net on our condensed consolidated statement of operations.
Convertible debt	Convertible debt
	We account for convertible debt instruments, including our 1 percent and 2¾ percent convertible notes, that may be settled in cash upon conversion (including partial cash settlement) by separating the liability and equity components of the instruments in a manner that reflects our nonconvertible debt borrowing rate. We determine the carrying amount of the liability component by measuring the fair value of similar debt instruments that do not have the conversion feature. If no similar debt instrument exists, we estimate fair value by using assumptions that market participants would use in pricing a debt instrument, including market interest rates, credit standing, yield curves and volatilities. Determining the fair value of the debt component requires the use of accounting estimates and assumptions. These estimates and assumptions are judgmental in nature and could have a significant impact on the determination of the debt component, and the associated non-cash interest expense.
	We assign a value to the debt component of our convertible notes equal to the estimated fair value of similar debt instruments without the conversion feature, which resulted in us recording our debt at a discount. We are amortizing the debt discount over the life of the convertible notes as additional non-cash interest expense utilizing the effective interest method.
Segment information	Segment information
	In 2015, we began operating as two segments, our Isis Core segment, previously referred to as Drug Discovery and Development, and our new segment, Akcea Therapeutics, which includes the operations of our newly-formed and wholly-owned subsidiary, Akcea Therapeutics, Inc. We formed Akcea to develop and commercialize the drugs from our lipid franchise. We provide segment financial information and results for our Isis Core segment and our Akcea Therapeutics segment based on the segregation of revenues and expenses that our chief decision maker reviews to assess operating performance and to make operating decisions. We use judgments and estimates in determining the allocation of shared expenses to the two segments. Different assumptions or allocation methods could result in materially different results by segment.
Stock-based compensation expense	Stock-based compensation expense
	We measure stock-based compensation expense for equity-classified awards, principally related to stock options, restricted stock units, or RSUs, and stock purchase rights under our ESPP, based on the estimated fair value of the award on the date of grant. We recognize the value of the portion of the award that we ultimately expect to vest as stock-based compensation expense over the requisite service period in our condensed consolidated statements of operations. We reduce stock-based compensation expense for estimated forfeitures at the time of grant and revise in subsequent periods if actual forfeitures differ from those estimates.
	We use the Black-Scholes model to estimate the fair value of stock options granted and stock purchase rights under our ESPP. The expected term of stock options granted represents the period of time that we expect them to be outstanding. We estimate the expected term of options granted based on historical exercise patterns. For the three months ended March 31, 2015 and 2014, we used the following weighted-average assumptions in our Black-Scholes calculations:
	Employee Stock Options:
		Three Months Ended
		March 31,
		2015			2014
	Risk-free interest rate		1.50%			1.60%
	Dividend yield		0.00%			0.00%
	Volatility		53.50%			50.50%
	Expected life		4.5 years			4.6 years
	ESPP:
		Three Months Ended
		March 31,
		2015			2014
	Risk-free interest rate		0.10%			0.10%
	Dividend yield		0.00%			0.00%
	Volatility		56.20%			59.00%
	Expected life		6 months			6 months
	Board of Director Stock Options:
			Three Months Ended
			31-Mar-14
	Risk-free interest rate			2.3	%
	Dividend yield			0	%
	Volatility			53.3	%
	Expected life		7.1 years
	The fair value of RSUs is based on the market price of our common stock on the date of grant. RSUs vest annually over a four year period. The weighted-average grant date fair value of RSUs granted to employees for the three months ended March 31, 2015 was $68.84 per share.
	We did not grant any stock options or RSUs to the Board of Directors for the three months ended March 31, 2015.
	The following table summarizes stock-based compensation expense for the three months ended March 31, 2015 and 2014 (in thousands), which was allocated as follows:
		Three Months Ended
		March 31,
		2015				2014
	Research, development and patent expenses		$	10,486			$	5,873
	General and administrative			2,819				1,196
	Total		$	13,305			$	7,069
	Non-cash stock-based compensation expense was $13.3 million for the three months ended March 31, 2015, and increased compared to $7.1 million for the same period in 2014 primarily due to the increase in our stock price. As of March 31, 2015, total unrecognized estimated non-cash stock-based compensation expense related to non-vested stock options and RSUs was $60.2 million and $25.0 million, respectively. We will adjust total unrecognized compensation cost for future changes in estimated forfeitures. We expect to recognize the cost of non-cash, stock-based compensation expense related to non-vested stock options and RSUs over a weighted average amortization period of 1.5 years and 1.8 years, respectively.
Impact of recently issued accounting standards	Impact of recently issued accounting standards
	In May 2014, the FASB issued accounting guidance on the recognition of revenue from customers. Under this guidance, an entity will recognize revenue when it transfers promised goods or services to customers in an amount that reflects what the entity expects in exchange for the goods or services. This guidance also requires more detailed disclosures to enable users of the financial statements to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The guidance as currently issued is effective for fiscal years, and interim periods within that year, beginning after December 15, 2016 and will be effective for us in our fiscal year beginning January 1, 2017. On April 1, 2015, the FASB voted to propose deferring the effective date by one year. The FASB would still permit entities to choose to adopt on the original effective date. The proposal is subject to the FASB’s due process requirement, which includes a period for public comment. The guidance allows us to select one of two methods of adoption, either the full retrospective approach, meaning the guidance would be applied to all periods presented, or modified retrospective, meaning the cumulative effect of applying the guidance would be recognized as an adjustment to our opening retained earnings balance. We are currently in the process of determining the adoption method and timing as well as the effects the adoption will have on our consolidated financial statements and disclosures.
	In August 2014, the FASB issued accounting guidance on how and when to disclose going-concern uncertainties in the financial statements. This guidance will require us to perform interim and annual assessments to determine our ability to continue as a going concern within one year from the date that we issue our financial statements. The guidance is effective for fiscal years, and interim periods within that year, beginning after December 15, 2016. We will adopt this guidance in our fiscal year beginning January 1, 2017. We do not expect this guidance to have any effect on our financial statements.
	In February 2015, the FASB issued accounting guidance which amends existing consolidation guidance for entities that are required to evaluate whether they should consolidate certain legal entities. The guidance is effective for fiscal years, and interim periods within that year, beginning after December 15, 2015. We will adopt this guidance in our fiscal year beginning January 1, 2016. We do not expect this guidance to have any effect on our financial statements.
	In April 2015, the FASB issued accounting guidance to simplify the presentation of debt issuance costs. The amended guidance requires us to present debt issuance costs as a direct deduction from the carrying amount of the related debt liability rather than as an asset. The guidance does not require us to change how we recognize and measure our debt issuance costs. The guidance is effective for fiscal years, and interim periods within that year, beginning after December 15, 2015. We will adopt this guidance in our fiscal year beginning January 1, 2016. We do not expect this guidance to have a material impact on our financial statements.
	In April 2015, the FASB issued accounting guidance to clarify the accounting for fees paid in cloud computing arrangements. The amendment provides guidance to customers about whether a cloud computing arrangement includes a software license element consistent with the acquisition of other software licenses or if the arrangement excludes a software license and should be accounted for as a service contract. The guidance does not change the accounting for service contracts. The guidance is effective for fiscal years, and interim periods within that year, beginning after December 15, 2015. We can choose to adopt it either prospectively or retrospectively. We will adopt this guidance in our fiscal year beginning January 1, 2016. We are currently evaluating the impact, if any, of the adoption of this newly issued guidance to our condensed consolidated financial statements.

Significant_Accounting_Policie2

Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2015
Significant Accounting Policies [Abstract]
Changes in accumulated other comprehensive income related to unrealized gains and losses on securities	Accumulated other comprehensive income is comprised of unrealized gains and losses on investments, net of taxes, and adjustments we made to reclassify realized gains and losses on investments from other accumulated comprehensive income to our condensed consolidated statement of operations. The following table summarizes changes in accumulated other comprehensive income for the three months ended March 31, 2015 and 2014 (in thousands):
			Three Months Ended
			March 31,
			2015				2014
	Beginning balance accumulated other comprehensive income		$	39,747			$	21,080
	Other comprehensive income before reclassifications, net of tax (1)			7,367				8,261
	Amounts reclassified from accumulated other comprehensive income (2)			—				(341	)
	Net current period other comprehensive income			7,367				7,920
	Ending balance accumulated other comprehensive income		$	47,114			$	29,000
		-1	Other comprehensive income from the three months ended March 31, 2015 includes income tax expense of $5.1 million, compared to $5.4 million for the three months ended March 31, 2014.
		-2	Included in gain on investments, net on our condensed consolidated statement of operations.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of weighted-average assumptions used for valuation of ESPP	ESPP:
		Three Months Ended
		March 31,
		2015			2014
	Risk-free interest rate		0.10%			0.10%
	Dividend yield		0.00%			0.00%
	Volatility		56.20%			59.00%
	Expected life		6 months			6 months
Schedule of stock-based compensation expense	The following table summarizes stock-based compensation expense for the three months ended March 31, 2015 and 2014 (in thousands), which was allocated as follows:
		Three Months Ended
		March 31,
		2015				2014
	Research, development and patent expenses		$	10,486			$	5,873
	General and administrative			2,819				1,196
	Total		$	13,305			$	7,069
Employee Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of weighted-average assumptions used for valuation of stock options	We use the Black-Scholes model to estimate the fair value of stock options granted and stock purchase rights under our ESPP. The expected term of stock options granted represents the period of time that we expect them to be outstanding. We estimate the expected term of options granted based on historical exercise patterns. For the three months ended March 31, 2015 and 2014, we used the following weighted-average assumptions in our Black-Scholes calculations:
	Employee Stock Options:
		Three Months Ended
		March 31,
		2015			2014
	Risk-free interest rate		1.50%			1.60%
	Dividend yield		0.00%			0.00%
	Volatility		53.50%			50.50%
	Expected life		4.5 years			4.6 years
Board of Director Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of weighted-average assumptions used for valuation of stock options	Board of Director Stock Options:
			Three Months Ended
			31-Mar-14
	Risk-free interest rate			2.3	%
	Dividend yield			0	%
	Volatility			53.3	%
	Expected life		7.1 years

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Investments [Abstract]
Summary of contract maturity of available-for-sale securities	The following table summarizes the contract maturity of the available-for-sale securities we held as of March 31, 2015:
	One year or less	58%
	After one year but within two years	29%
	After two years but within three years	13%
	Total	100%
Summary of investments	The following is a summary of our investments (in thousands):
			Amortized			Gross Unrealized							Other-				Estimated
													Than-
													Temporary
													Impairment
	31-Mar-15		Cost			Gains			Losses				Loss				Fair Value
	Available-for-sale securities:
	Corporate debt securities		$	190,437		$	87		$	(31	)		$	—			$	190,493
	Debt securities issued by U.S. government agencies			53,006			5			(13	)			—				52,998
	Debt securities issued by the U.S. Treasury			5,999			4			—				—				6,003
	Debt securities issued by states of the United States and political subdivisions of the states (1)			46,571			25			(50	)			—				46,546
	Total securities with a maturity of one year or less			296,014			121			(94	)			—				296,040
	Corporate debt securities			137,653			124			(162	)			—				137,615
	Debt securities issued by U.S. government agencies			62,529			29			(14	)			—				62,544
	Debt securities issued by states of the United States and political subdivisions of the states			59,667			48			(165	)			—				59,550
	Total securities with a maturity of more than one year			259,849			201			(341	)			—				259,709
	Total available-for-sale securities		$	555,862		$	322		$	(435	)		$	—			$	555,749
		Cost			Gross Unrealized							Other-				Estimated
												Than-
												Temporary
												Impairment
	31-Mar-15	Basis			Gains			Losses				Loss				Fair Value
	Equity securities:
	Regulus Therapeutics Inc.		$	12,477		$	80,969		$	—			$	—			$	93,446
	Securities included in other current assets			880			—			—				(880	)			—
	Total equity securities		$	13,357		$	80,969		$	—			$	(880	)		$	93,446
	Total available-for-sale and equity securities		$	569,220		$	81,291		$	(435	)		$	(880	)		$	649,195
			Amortized			Gross Unrealized							Other-				Estimated
													Than-
													Temporary
													Impairment
	31-Dec-14		Cost			Gains			Losses				Loss				Fair Value
	Available-for-sale securities:
	Corporate debt securities(1)		$	219,856		$	89		$	(89	)		$	—			$	219,856
	Debt securities issued by U.S. government agencies			47,496			7			(27	)			—				47,476
	Debt securities issued by the U.S. Treasury (1)			19,008			9			—				—				19,017
	Debt securities issued by states of the United States and political subdivisions of the states (1)			45,196			19			(53	)			—				45,162
	Total securities with a maturity of one year or less			331,556			124			(169	)			—				331,511
	Corporate debt securities			152,730			16			(600	)			—				152,146
	Debt securities issued by U.S. government agencies			62,530			—			(151	)			—				62,379
	Debt securities issued by states of the United States and political subdivisions of the states			60,073			32			(234	)			—				59,871
	Total securities with a maturity of more than one year			275,333			48			(985	)			—				274,396
	Total available-for-sale securities		$	606,889		$	172		$	(1,154	)		$	—			$	605,907
		Cost			Gross Unrealized							Other-				Estimated
												Than-
												Temporary
												Impairment
	31-Dec-14	Basis			Gains			Losses				Loss				Fair Value
	Equity securities:
	Regulus Therapeutics Inc.		$	12,477		$	69,404		$	—			$	—			$	81,881
	Securities included in other current assets			880			—			—				(880	)			—
	Total equity securities		$	13,357		$	69,404		$	—			$	(880	)		$	81,881
	Total available-for-sale and equity securities		$	620,246		$	69,576		$	(1,154	)		$	(880	)		$	687,788
		-1	Includes investments classified as cash equivalents on our condensed consolidated balance sheet.
Schedule of investments temporarily impaired	Investments we considered to be temporarily impaired at March 31, 2015 were as follows (in thousands):
						Less than 12 months of							More than 12 months of							Total temporary
						temporary impairment							temporary impairment							impairment
			Number of			Estimated			Unrealized				Estimated				Unrealized			Estimated		Unrealized
			Investments			Fair Value			Losses				Fair Value				Losses			Fair Value		Losses
	Corporate debt securities			132		$	136,603		$	(193	)		$	—			$	—		$	136,603	$	(193	)
	Debt securities issued by U.S. government agencies			11			74,094			(27	)			—				—			74,094		(27	)
	Debt securities issued by states of the United States and political subdivisions of the states			24			42,943			(144	)			6,231				(71	)		49,174		(215	)
	Total temporarily impaired securities			167		$	253,640		$	(364	)		$	6,231			$	(71	)	$	259,871	$	(435	)

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Measurements [Abstract]
Schedule of assets measured at fair value on a recurring basis	We measure the following major security types at fair value on a recurring basis. The following summary breaks down the fair-value hierarchy that we used to value each security at March 31, 2015 and December 31, 2014 (in thousands):
			At			Quoted Prices in		Significant Other		Significant
			March 31,			Active Markets		Observable		Unobservable
			2015			(Level 1)		Inputs		Inputs
								(Level 2)		(Level 3)
	Cash equivalents (1)		$	112,777		$	112,777	$	—	$	—
	Corporate debt securities (2)			328,108			—		328,108		—
	Debt securities issued by U.S. government agencies (2)			115,542			—		115,542		—
	Debt securities issued by the U.S. Treasury (2)			6,003			6,003		—		—
	Debt securities issued by states of the United States and political subdivisions of the states (3)			106,096			—		106,096		—
	Investment in Regulus Therapeutics Inc.			93,446			93,446		—		—
	Total		$	761,972		$	212,226	$	549,746	$	—
			At			Quoted Prices in		Significant Other		Significant
			December 31,			Active Markets		Observable		Unobservable
			2014			(Level 1)		Inputs		Inputs
								(Level 2)		(Level 3)
	Cash equivalents (1)		$	104,680		$	104,680	$	—	$	—
	Corporate debt securities (4)			372,002			—		372,002		—
	Debt securities issued by U.S. government agencies (2)			109,855			—		109,855		—
	Debt securities issued by the U.S. Treasury (5)			19,017			19,017		—		—
	Debt securities issued by states of the United States and political subdivisions of the states (6)			105,033			—		105,033		—
	Investment in Regulus Therapeutics Inc.			81,881			—		—		81,881
	Total		$	792,468		$	123,697	$	586,890	$	81,881
		-1	Included in cash and cash equivalents on our condensed consolidated balance sheet.
		-2	Included in short-term investments on our condensed consolidated balance sheet.
		-3	$9.0 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
		-4	$0.8 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
		-5	$10 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
		-6	$9.3 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
Summary of investments measured at fair value on a recurring basis using significant unobservable inputs (Level 3)	The following is a summary of our investments measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the three months ended March 31, 2015 (in thousands):
	Beginning balance of Level 3 investments		$	81,881
	Total gain included in accumulated other comprehensive income (loss)			22,377
	Transfers out of Level 3 investments			(104,258	)
	Ending balance of Level 3 investments		$	—

Segment_Information_and_Concen1

Segment Information and Concentration of Business Risk (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Information and Concentration of Business Risk [Abstract]
Segment Information	The following is our segment information for the three months ended March 31, 2015 (in thousands).
		Isis Core				Akcea Therapeutics				Total
	Revenue:
	Research and development		$	61,892			$	—			$	61,892
	Licensing and royalty			691				—				691
	Total segment revenue		$	62,583			$	—			$	62,583
	Loss from operations		$	(2,232	)		$	(7,098	)		$	(9,330	)
Schedule of revenue from significant partners	We have historically funded our operations from collaborations with corporate partners and a relatively small number of partners have accounted for a significant percentage of our revenue. Revenue from significant partners, which is defined as ten percent or more of our total revenue, was as follows:
		Three Months Ended
		March 31,
		2015			2014
	Partner A		63%			36%
	Partner B		26%			12%
	Partner C		1%			12%
	Partner D		0%			27%

Significant_Accounting_Policie3

Significant Accounting Policies, Revenue Recognition (Details) (USD $)	3 Months Ended		1 Months Ended		7 Months Ended	1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013	Jan. 31, 2012	Jun. 30, 2012	Sep. 30, 2013
				AccountingUnit
				Target
Collaborative Arrangements and Licensing Agreements [Line Items]
Licensing and royalty revenue	$691,000	$8,611,000
Collaborations and Licensing Agreements [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Number of categories of milestone events	3
Number of stages of life-cycle of drugs	3
Collaborations and Licensing Agreements [Member] | Development milestones - new development candidate [Member] | Minimum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Completion period	12 months
Collaborations and Licensing Agreements [Member] | Development milestones - new development candidate [Member] | Maximum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Completion period	18 months
Collaborations and Licensing Agreements [Member] | Development milestones - Phase 1 [Member] | Minimum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Completion period	1 year
Collaborations and Licensing Agreements [Member] | Development milestones - Phase 1 [Member] | Maximum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Completion period	2 years
Collaborations and Licensing Agreements [Member] | Development milestones - Phase 2 [Member] | Minimum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Completion period	1 year
Collaborations and Licensing Agreements [Member] | Development milestones - Phase 2 [Member] | Maximum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Completion period	3 years
Collaborations and Licensing Agreements [Member] | Development milestones - Phase 3 [Member] | Minimum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Completion period	2 years
Collaborations and Licensing Agreements [Member] | Development milestones - Phase 3 [Member] | Maximum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Completion period	4 years
Collaborations and Licensing Agreements [Member] | Regulatory Milestones [Member] | Minimum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Time to prepare and submit regulatory filings	6 months
Time to obtain approval	1 year
Collaborations and Licensing Agreements [Member] | Regulatory Milestones [Member] | Maximum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Time to prepare and submit regulatory filings	12 months
Time to obtain approval	2 years
Collaborations and Licensing Agreements [Member] | Commercialization Milestones [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Example of sales threshold as milestone event	1,000,000,000
AstraZeneca [Member] | Agreement Entered into in December 2012 [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Number of targets				5
Upfront fee received			6,000,000	25,000,000	31,000,000
Number of units of accounting				4
AstraZeneca [Member] | Agreement Entered into in December 2012 [Member] | Maximum [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Number of drugs collaborative partner may license under the separate research program				3
AstraZeneca [Member] | Agreement Entered into in December 2012 [Member] | ISIS-AR [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Number of units of accounting				1
Biogen Idec [Member] | Collaborations and Licensing Agreements [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Number of collaborative agreements	4
Biogen Idec [Member] | Agreement Entered into in January 2012 [Member] | ISIS-SMN [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Upfront fee recorded as deferred revenue						29,000,000
Biogen Idec [Member] | Agreement Entered into in June 2012 [Member] | ISIS-DMPK [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Upfront fee recorded as deferred revenue							12,000,000
Biogen Idec [Member] | Agreement Entered into in December 2012 [Member] | Neurology [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Number of targets				3
Upfront fee recorded as deferred revenue				30,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Upfront fee recorded as deferred revenue								100,000,000
Term of collaboration agreement	6 years
Alnylam [Member] | Alnylam's collaboration with Genzyme [Member]
Collaborative Arrangements and Licensing Agreements [Line Items]
Licensing and royalty revenue		$7,700,000

Significant_Accounting_Policie4

Significant Accounting Policies, Cash, Cash Equivalents and Short-term Investments, Inventory Valuation, and Research, Development and Patent Expenses (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Inventory valuation [Abstract]
Raw materials	6,839	$6,290
Maximum [Member] | Privately- and Publicly-Held Biotechnology Companies [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in equity investments (in hundredths)	20.00%

Significant_Accounting_Policie5

Significant Accounting Policies, Consolidation of Variable Interest Entities (Details) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2013
	Entity	Entity
Consolidation of variable interest entities [Abstract]
Number of variable interest entities in which the entity is not primary beneficiary	2	2
Carrying value of investments in variable interest entities	$93.40

Significant_Accounting_Policie6

Significant Accounting Policies, Accumulated Other Comprehensive Income (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Summary of changes in accumulated other comprehensive income [Roll Forward]
Beginning balance accumulated other comprehensive income	$39,747,000		$21,080,000
Other comprehensive income before reclassifications, net of tax	7,367,000	[1]	8,261,000	[1]
Amounts reclassified from accumulated other comprehensive income	0	[2]	-341,000	[2]
Net current period other comprehensive income	7,367,000		7,920,000
Ending balance accumulated other comprehensive income	47,114,000		29,000,000
Income tax expense (benefit) included in other comprehensive income	$5,100,000		$5,400,000
[1]	Other comprehensive income from the three months ended March 31, 2015 includes income tax expense of $5.1 million, compared to $5.4 million for the three months ended March 31, 2014.
[2]	Included in gain on investments, net on our condensed consolidated statement of operations.

Significant_Accounting_Policie7

Significant Accounting Policies, Convertible Debt and Segment Information (Details)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
	Segment
Segment Information [Abstract]
Number of operating segments	2
1 Percent Convertible Senior Notes [Member]
Convertible Debt [Abstract]
Interest rate on convertible debt (in hundredths)	1.00%	1.00%
2 3/4 Percent Convertible Senior Notes [Member]
Convertible Debt [Abstract]
Interest rate on convertible debt (in hundredths)	2.75%	2.75%	2.75%

Significant_Accounting_Policie8

Significant Accounting Policies, Stock-Based Compensation Expense - Weighted-Average Assumptions (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Employee Stock Options [Member]
Weighted-average assumptions [Abstract]
Risk-free interest rate (in hundredths)	1.50%	1.60%
Dividend yield (in hundredths)	0.00%	0.00%
Volatility (in hundredths)	53.50%	50.50%
Expected life	4 years 6 months	4 years 7 months 6 days
ESPP [Member]
Weighted-average assumptions [Abstract]
Risk-free interest rate (in hundredths)	0.10%	0.10%
Dividend yield (in hundredths)	0.00%	0.00%
Volatility (in hundredths)	56.20%	59.00%
Expected life	6 months	6 months
Board of Director Stock Options [Member]
Weighted-average assumptions [Abstract]
Risk-free interest rate (in hundredths)		2.30%
Dividend yield (in hundredths)		0.00%
Volatility (in hundredths)		53.30%
Expected life		7 years 1 month 6 days

Significant_Accounting_Policie9

Significant Accounting Policies, Stock-Based Compensation Expense (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$13,305,000	$7,069,000
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Unrecognized estimated non-cash stock-based compensation expense	60,200,000
Weighted average period of amortization	1 year 6 months
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Vesting period	4 years
Unrecognized estimated non-cash stock-based compensation expense	25,000,000
Weighted average period of amortization	1 year 9 months 18 days
RSUs [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Weighted-average grant date fair value (in dollars per share)	$68.84
Research, Development and Patent Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	10,486,000	5,873,000
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$2,819,000	$1,196,000

Investments_Contract_Maturity_

Investments, Contract Maturity of Available-for-Sale Securities (Details)	Mar. 31, 2015
	Company
Contract maturity of available-for-sale securities [Abstract]
One year or less (in hundredths)	58.00%
After one year but within two years (in hundredths)	29.00%
After two years but within three years (in hundredths)	13.00%
Total (in hundredths)	100.00%
Percentage of available-for-sale securities with a maturity of less than two years (in hundredths)	87.00%
Ownership interests in private and public companies [Abstract]
Number of privately-held companies in which the entity has an equity ownership interest of less than 20%	1
Number of publicly-held companies in which the entity has an equity ownership interest of less than 20%	2

Investments_Summary_of_Investm

Investments, Summary of Investments and Investments Temporarily Impaired (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Thousands, unless otherwise specified	Investment
Investment Holdings [Line Items]
Cost basis	$569,220		$620,246
Gross unrealized gains	81,291		69,576
Gross unrealized losses	-435		-1,154
Other-than-temporary impairment loss	-880		-880
Estimated fair value	649,195		687,788
Temporarily impaired investments [Abstract]
Temporarily impaired securities, Number of Investments	167
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated fair value	253,640
Temporarily impaired securities, Less than 12 months of temporary impairment, Unrealized losses	-364
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated fair value	6,231
Temporarily impaired securities, More than 12 months of temporary impairment, Unrealized losses	-71
Total temporary impairment, Estimated fair value	259,871
Total temporary impairment, Unrealized losses	-435
Available-for-sale securities [Member]
Investment Holdings [Line Items]
Amortized cost	555,862		606,889
Gross unrealized gains	322		172
Gross unrealized losses	-435		-1,154
Other-than-temporary impairment loss	0		0
Estimated fair value	555,749		605,907
Available-for-sale securities [Member] | Debt maturities of one year or less [Member]
Investment Holdings [Line Items]
Amortized cost	296,014		331,556
Gross unrealized gains	121		124
Gross unrealized losses	-94		-169
Other-than-temporary impairment loss	0		0
Estimated fair value	296,040		331,511
Available-for-sale securities [Member] | Debt maturities of more than one year [Member]
Investment Holdings [Line Items]
Amortized cost	259,849		275,333
Gross unrealized gains	201		48
Gross unrealized losses	-341		-985
Other-than-temporary impairment loss	0		0
Estimated fair value	259,709		274,396
Corporate Debt Securities [Member]
Temporarily impaired investments [Abstract]
Temporarily impaired securities, Number of Investments	132
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated fair value	136,603
Temporarily impaired securities, Less than 12 months of temporary impairment, Unrealized losses	-193
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated fair value	0
Temporarily impaired securities, More than 12 months of temporary impairment, Unrealized losses	0
Total temporary impairment, Estimated fair value	136,603
Total temporary impairment, Unrealized losses	-193
Corporate Debt Securities [Member] | Debt maturities of one year or less [Member]
Investment Holdings [Line Items]
Amortized cost	190,437	[1]	219,856	[1]
Gross unrealized gains	87	[1]	89	[1]
Gross unrealized losses	-31	[1]	-89	[1]
Other-than-temporary impairment loss	0	[1]	0	[1]
Estimated fair value	190,493	[1]	219,856	[1]
Corporate Debt Securities [Member] | Debt maturities of more than one year [Member]
Investment Holdings [Line Items]
Amortized cost	137,653		152,730
Gross unrealized gains	124		16
Gross unrealized losses	-162		-600
Other-than-temporary impairment loss	0		0
Estimated fair value	137,615		152,146
Debt Securities issued by U.S. Government Agencies [Member]
Temporarily impaired investments [Abstract]
Temporarily impaired securities, Number of Investments	11
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated fair value	74,094
Temporarily impaired securities, Less than 12 months of temporary impairment, Unrealized losses	-27
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated fair value	0
Temporarily impaired securities, More than 12 months of temporary impairment, Unrealized losses	0
Total temporary impairment, Estimated fair value	74,094
Total temporary impairment, Unrealized losses	-27
Debt Securities issued by U.S. Government Agencies [Member] | Debt maturities of one year or less [Member]
Investment Holdings [Line Items]
Amortized cost	53,006	[1]	47,496	[1]
Gross unrealized gains	5	[1]	7	[1]
Gross unrealized losses	-13	[1]	-27	[1]
Other-than-temporary impairment loss	0	[1]	0	[1]
Estimated fair value	52,998	[1]	47,476	[1]
Debt Securities issued by U.S. Government Agencies [Member] | Debt maturities of more than one year [Member]
Investment Holdings [Line Items]
Amortized cost	62,529		62,530
Gross unrealized gains	29		0
Gross unrealized losses	-14		-151
Other-than-temporary impairment loss	0		0
Estimated fair value	62,544		62,379
Debt Securities issued by the U.S. Treasury [Member] | Debt maturities of one year or less [Member]
Investment Holdings [Line Items]
Amortized cost	5,999		19,008
Gross unrealized gains	4		9
Gross unrealized losses	0		0
Other-than-temporary impairment loss	0		0
Estimated fair value	6,003		19,017
Debt Securities issued by States of the United States and Political Subdivisions of the States [Member]
Temporarily impaired investments [Abstract]
Temporarily impaired securities, Number of Investments	24
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated fair value	42,943
Temporarily impaired securities, Less than 12 months of temporary impairment, Unrealized losses	-144
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated fair value	6,231
Temporarily impaired securities, More than 12 months of temporary impairment, Unrealized losses	-71
Total temporary impairment, Estimated fair value	49,174
Total temporary impairment, Unrealized losses	-215
Debt Securities issued by States of the United States and Political Subdivisions of the States [Member] | Debt maturities of one year or less [Member]
Investment Holdings [Line Items]
Amortized cost	46,571	[1]	45,196	[1]
Gross unrealized gains	25	[1]	19	[1]
Gross unrealized losses	-50	[1]	-53	[1]
Other-than-temporary impairment loss	0	[1]	0	[1]
Estimated fair value	46,546	[1]	45,162	[1]
Debt Securities issued by States of the United States and Political Subdivisions of the States [Member] | Debt maturities of more than one year [Member]
Investment Holdings [Line Items]
Amortized cost	59,667		60,073
Gross unrealized gains	48		32
Gross unrealized losses	-165		-234
Other-than-temporary impairment loss	0		0
Estimated fair value	59,550		59,871
Equity Securities [Member]
Investment Holdings [Line Items]
Cost basis	13,357		13,357
Gross unrealized gains	80,969		69,404
Gross unrealized losses	0		0
Other-than-temporary impairment loss	-880		-880
Estimated fair value	93,446		81,881
Equity Securities [Member] | Securities included in other current assets [Member]
Investment Holdings [Line Items]
Cost basis	880		880
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Other-than-temporary impairment loss	-880		-880
Estimated fair value	0		0
Equity Securities [Member] | Regulus Therapeutics Inc. [Member]
Investment Holdings [Line Items]
Cost basis	12,477		12,477
Gross unrealized gains	80,969		69,404
Gross unrealized losses	0		0
Other-than-temporary impairment loss	0		0
Estimated fair value	$93,446		$81,881
[1]	Includes investments classified as cash equivalents on our condensed consolidated balance sheet.

Fair_Value_Measurements_Assets

Fair Value Measurements, Assets Measured at Fair Value on a Recurring Basis (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
Fair Value Measurements [Abstract]
Amount of transfer between Level 1 and Level 2 investments	$0
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in Regulus Therapeutics Inc.	93,446,000		81,881,000
2 3/4 Percent Convertible Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on convertible debt (in hundredths)	2.75%		2.75%		2.75%
Fair value of convertible notes	233,700,000
1 Percent Convertible Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on convertible debt (in hundredths)	1.00%		1.00%
Fair value of convertible notes	584,700,000
Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	112,777,000	[1]	104,680,000	[1]
Investment in Regulus Therapeutics Inc.	93,446,000		81,881,000
Total assets	761,972,000		792,468,000
Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	328,108,000	[2]	372,002,000	[3]
Recurring Basis [Member] | Corporate Debt Securities [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities			800,000
Recurring Basis [Member] | Debt Securities issued by U.S. Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	115,542,000	[2]	109,855,000	[2]
Recurring Basis [Member] | Debt Securities issued by the U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6,003,000	[2]	19,017,000	[4]
Recurring Basis [Member] | Debt Securities issued by the U.S. Treasury [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities			10,000,000
Recurring Basis [Member] | Debt Securities issued by States of the United States and Political Subdivisions of the States [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	106,096,000	[5]	105,033,000	[6]
Recurring Basis [Member] | Debt Securities issued by States of the United States and Political Subdivisions of the States [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9,000,000		9,300,000
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	112,777,000	[1]	104,680,000	[1]
Investment in Regulus Therapeutics Inc.	93,446,000		0
Total assets	212,226,000		123,697,000
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[2]	0	[3]
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities issued by U.S. Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[2]	0	[2]
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities issued by the U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6,003,000	[2]	19,017,000	[4]
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities issued by States of the United States and Political Subdivisions of the States [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[5]	0	[6]
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	[1]	0	[1]
Investment in Regulus Therapeutics Inc.	0		0
Total assets	549,746,000		586,890,000
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	328,108,000	[2]	372,002,000	[3]
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Debt Securities issued by U.S. Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	115,542,000	[2]	109,855,000	[2]
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Debt Securities issued by the U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[2]	0	[4]
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Debt Securities issued by States of the United States and Political Subdivisions of the States [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	106,096,000	[5]	105,033,000	[6]
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	[1]	0	[1]
Investment in Regulus Therapeutics Inc.	0		81,881,000
Total assets	0		81,881,000
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[2]	0	[3]
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Debt Securities issued by U.S. Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[2]	0	[2]
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Debt Securities issued by the U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[2]	0	[4]
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Debt Securities issued by States of the United States and Political Subdivisions of the States [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$0	[5]	0	[6]
[1]	Included in cash and cash equivalents on our condensed consolidated balance sheet.
[2]	Included in short-term investments on our condensed consolidated balance sheet.
[3]	$0.8 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
[4]	$10 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
[5]	$9.0 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.
[6]	$9.3 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.

Fair_Value_Measurements_Invest

Fair Value Measurements, Investments Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) (Investments Valued Using Level 3 Inputs [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
Investments Valued Using Level 3 Inputs [Member]
Investments measured at fair value on a recurring basis using significant unobservable inputs (Level 3) [Roll Forward]
Beginning balance of Level 3 investments	$81,881
Total gain included in accumulated other comprehensive income (loss)	22,377
Transfers out of Level 3 investments	-104,258
Ending balance of Level 3 investments	$0

Income_Taxes_Details

Income Taxes (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Taxes [Abstract]
Tax benefit related to unrealized gains on investments in available-for-sale securities recorded in continuing operations	($789,000)	($2,276,000)
Tax expense related to unrealized gains on investments in available-for-sale securities recorded in other comprehensive income	$5,100,000	$5,400,000

Collaborative_Arrangements_and1

Collaborative Arrangements and Licensing Agreements, Traditional Pharmaceutical Alliances and Licensing - Bayer HealthCare (Details) (Bayer HealthCare [Member], Agreement Entered into in April 2015 [Member], Subsequent Event [Member], USD $)	0 Months Ended
In Millions, unless otherwise specified	5-May-15
Collaborative Arrangement and Licensing Agreement [Abstract]
Near-term payments	$155
Upfront fee	100
Next prospective milestone	55
Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Percentage of gross margins of sales received as royalties (in hundredths)	20.00%
License Fees, Milestone Payments and Other Payments [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable	375
Development Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable	120
Commercialization Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable	$110

Collaborative_Arrangements_and2

Collaborative Arrangements and Licensing Agreements, Traditional Pharmaceutical Alliances and Licensing - Biogen Idec (ISIS-SMN) (Details) (Biogen Idec [Member], USD $)	3 Months Ended	1 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Jan. 31, 2012
ISIS-SMN [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Increase in payments that the Company is eligible to receive under collaboration	$57
Cumulative payments received	110
Next prospective milestone	8.5
ISIS-SMN [Member] | Phase 3 Study in Infants with SMA [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Milestone payment earned	9
ISIS-SMN [Member] | Open-Label Extension Study in Children with SMA [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Milestone payment earned	7
ISIS-SMN [Member] | License Fee and Substantive Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable	327
ISIS-SMN [Member] | Development Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable	102
ISIS-SMN [Member] | Regulatory Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable	150
Collaborations and Licensing Agreements [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of collaborative agreements	4
Agreement Entered into in January 2012 [Member] | ISIS-SMN [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Upfront fee recorded as deferred revenue		$29

Collaborative_Arrangements_and3

Collaborative Arrangements and Licensing Agreements, Traditional Pharmaceutical Alliances and Licensing - Biogen Idec (ISIS-DMPK) (Details) (Biogen Idec [Member], Agreement Entered into in June 2012 [Member], ISIS-DMPK [Member], USD $)	1 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2015
Collaborative Arrangement and Licensing Agreement [Abstract]
Upfront fee recorded as deferred revenue	$12
Cumulative payments received		36
Next prospective milestone		35
License Fee and Substantive Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable		259
Development Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable		59
Regulatory Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable		$130

Collaborative_Arrangements_and4

Collaborative Arrangements and Licensing Agreements, Traditional Pharmaceutical Alliances and Licensing - Biogen Idec (Neurology) (Details) (Biogen Idec [Member], Agreement Entered into in December 2012 [Member], Neurology [Member], USD $)	1 Months Ended
In Millions, unless otherwise specified	Feb. 28, 2015	Dec. 31, 2012	Mar. 31, 2015
		Program
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of programs under which drugs are to be developed and commercialized		3
Upfront fee recorded as deferred revenue		$30
Milestone payment earned	10
Cumulative payments received			40
Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Next prospective milestone			14
License Fee and Substantive Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable			259
Development Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable			59
Regulatory Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable			$130

Collaborative_Arrangements_and5

Collaborative Arrangements and Licensing Agreements, Traditional Pharmaceutical Alliances and Licensing - Biogen Idec (Strategic Neurology) (Details) (USD $)	3 Months Ended		1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2013	Apr. 30, 2015
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue earned	$62,583,000	$28,161,000
Biogen Idec [Member] | Collaborations and Licensing Agreements [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue earned	39,200,000	10,200,000
Percent of total revenue (in hundredths)	63.00%	36.00%
Deferred revenue	110,800,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Upfront fee recorded as deferred revenue			100,000,000
Period during which a change in control could result in requirement to refund upfront payment	6 years
Cumulative payments received	125,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member] | Subsequent Event [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Milestone payment earned				10,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member] | Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Next prospective milestone	10,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member] | Antisense Drug for Neurological Disease [Member] | License Fee and Substantive Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per drug	260,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member] | Antisense Drug for Neurological Disease [Member] | Research and Development Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per drug	60,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member] | Antisense Drug for Neurological Disease [Member] | Regulatory Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per drug	130,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member] | Other Modalities [Member] | Pre-specified Events [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per drug	90,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member] | Other Modalities [Member] | Research and Development Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per drug	35,000,000
Biogen Idec [Member] | Agreement Entered into in September 2013 [Member] | Strategic Neurology [Member] | Other Modalities [Member] | Regulatory Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per drug	$55,000,000

Collaborative_Arrangements_and6

Collaborative Arrangements and Licensing Agreements, Traditional Pharmaceutical Alliances and Licensing - GlaxoSmithKline (Details) (USD $)	1 Months Ended		3 Months Ended
	31-May-11	Mar. 31, 2010	Mar. 31, 2015	Mar. 31, 2014
			Drug
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue earned			$62,583,000	$28,161,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of drugs currently in development			5
Upfront fee received	3,000,000	35,000,000
Cumulative payments received			129,500,000
Revenue earned			16,500,000	3,300,000
Percent of total revenue (in hundredths)			26.00%	12.00%
Deferred revenue			9,200,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member] | Pre-specified Events [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Minimum amount of payments receivable			1,300,000,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member] | Development Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable			220,500,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member] | Regulatory Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable			483,500,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member] | Commercialization Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable			428,000,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member] | ISIS-TTR [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative milestone payments earned			60,000,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member] | ISIS-TTR [Member] | Development Milestones [Member] | Phase 2/3 Study [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Next prospective milestone			10,000,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member] | ISIS-GSK4 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Next prospective milestone			$5,000,000
Glaxo Smith Kline [Member] | Collaborations and Licensing Agreements [Member] | ISIS-HBV, ISIS-GSK4-L, ISIS-RHO-2.5, and ISIS-GSK6-L [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of drugs currently in development			4

Segment_Information_and_Concen2

Segment Information and Concentration of Business Risk (Details) (USD $)	3 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
	Segment		Partner
Segment Information and Concentration of Business Risk [Abstract]
Number of reportable segments	2
Revenues [Abstract]
Research and development revenue	$61,892	$19,550
Licensing and royalty	691	8,611
Total revenue	62,583	28,161
Loss from operations	-9,330	-29,667
Revenue [Member] | Partner A [Member]
Concentration Risk [Line Items]
Concentration percentage (in hundredths)	63.00%	36.00%
Revenue [Member] | Partner B [Member]
Concentration Risk [Line Items]
Concentration percentage (in hundredths)	26.00%	12.00%
Revenue [Member] | Partner C [Member]
Concentration Risk [Line Items]
Concentration percentage (in hundredths)	1.00%	12.00%
Revenue [Member] | Partner D [Member]
Concentration Risk [Line Items]
Concentration percentage (in hundredths)	0.00%	27.00%
Contract Receivables [Member] | Significant Partners [Member]
Concentration Risk [Line Items]
Concentration percentage (in hundredths)	92.00%		99.00%
Number of significant partners	2		3
Operating Segments [Member] | Isis Core [Member]
Revenues [Abstract]
Research and development revenue	61,892
Licensing and royalty	691
Total revenue	62,583
Loss from operations	-2,232
Operating Segments [Member] | Akcea [Member]
Revenues [Abstract]
Research and development revenue	0
Licensing and royalty	0
Total revenue	0
Loss from operations	($7,098)