Litigation	6 Months Ended
Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Litigation	Litigation The Company records an estimate of a loss when the loss is considered probable and estimable. Where a liability is probable and there is a range of estimated loss and no amount in the range is more likely than any other number in the range, the Company records the minimum estimated liability related to the claim in accordance with FASB ASC Topic 450 Contingencies. As additional information becomes available, the Company assesses the potential liability related to its pending litigation and revises its estimates. Revisions in the Company's estimates of potential liability could materially impact its results of operations. On July 27, 2018, AG Oncon, LLC, AG Ofcon, Ltd., Calamos Market Neutral Income Fund, Capital Ventures International, Citadel Equity Fund Ltd., Opti Opportunity Master Fund, Polygon Convertible Opportunity Master Fund, Wolverine Flagship Fund Trading Limited, as plaintiffs, filed a complaint in the Court of Chancery of the State of Delaware (AG Oncon, LLC v. Ligand Pharmaceuticals Inc.) alleging claims for violation of the Trust Indenture Act, breach of contract, damages and a declaratory judgment that the Supplemental Indenture, dated as of February 20, 2018, entered into by us and Wilmington Trust, National Association, as trustee, is invalid. The Supplemental Indenture supplemented the Indenture, dated as of August 18, 2014, between us and Wilmington Trust, National Association, which governs the 2019 Notes (as further supplemented, the “Indenture”). The Supplemental Indenture corrected a scrivener’s error in the conversion calculation of the 2019 Notes and was entered into pursuant to Section 9.01(b) of the Indenture, which expressly permits amendments to the Indenture without consent of the noteholders to conform the terms of the Indenture or the 2019 Notes to the “Description of the Notes” section of the offering memorandum for the 2019 Notes, which contained the correct conversion calculation. In addition, the correction conforms the calculation to the stated number of shares to be received upon conversion of the 2019 Notes that is stated in Section 10.01(a) of the Indenture, or a conversion rate initially equal to 13.3251 shares of common stock per $1,000 in principal amount of 2019 Notes. Notice of the Supplemental Indenture was provided to the holders of the 2019 Notes on March 8, 2018 in accordance with Section 9.04 of the Indenture. We believe the allegations are completely without merit, reject all claims raised by the plaintiffs and intend to vigorously defend this matter. In November 2017, CyDex, our wholly owned subsidiary, received a paragraph IV certification from Teva Pharmaceuticals USA, Inc., Teva Pharmaceutical Industries Ltd. and Actavis, LLC (collectively “Teva”) alleging that certain of our patents related to Captisol were invalid, unenforceable and/or will not be infringed by Teva’s ANDA related to Spectrum Pharmaceuticals’ NDA for Evomela. On December 20, 2017, CyDex filed a complaint against Teva in the U.S. District Court for the District of Delaware, asserting that Teva’s ANDA would infringe our patents. On March 22, Teva filed an answer and counterclaims seeking declarations of non-infringement and invalidity as to each of the asserted patents and on April 12, CyDex filed an answer to Teva’s counterclaims.

Litigation

The Company records an estimate of a loss when the loss is considered probable and estimable. Where a liability is probable and there is a range of estimated loss and no amount in the range is more likely than any other number in the range, the Company records the minimum estimated liability related to the claim in accordance with FASB ASC Topic 450 Contingencies. As additional information becomes available, the Company assesses the potential liability related to its pending litigation and revises its estimates. Revisions in the Company's estimates of potential liability could materially impact its results of operations.

On July 27, 2018, AG Oncon, LLC, AG Ofcon, Ltd., Calamos Market Neutral Income Fund, Capital Ventures International, Citadel Equity Fund Ltd., Opti Opportunity Master Fund, Polygon Convertible Opportunity Master Fund, Wolverine Flagship Fund Trading Limited, as plaintiffs, filed a complaint in the Court of Chancery of the State of Delaware (AG Oncon, LLC v. Ligand Pharmaceuticals Inc.) alleging claims for violation of the Trust Indenture Act, breach of contract, damages and a declaratory judgment that the Supplemental Indenture, dated as of February 20, 2018, entered into by us and Wilmington Trust, National Association, as trustee, is invalid. The Supplemental Indenture supplemented the Indenture, dated as of August 18, 2014, between us and Wilmington Trust, National Association, which governs the 2019 Notes (as further supplemented, the “Indenture”). The Supplemental Indenture corrected a scrivener’s error in the conversion calculation of the 2019 Notes and was entered into pursuant to Section 9.01(b) of the Indenture, which expressly permits amendments to the Indenture without consent of the noteholders to conform the terms of the Indenture or the 2019 Notes to the “Description of the Notes” section of the offering memorandum for the 2019 Notes, which contained the correct conversion calculation. In addition, the correction conforms the calculation to the stated number of shares to be received upon conversion of the 2019 Notes that is stated in Section 10.01(a) of the Indenture, or a conversion rate initially equal to 13.3251 shares of common stock per $1,000 in principal amount of 2019 Notes. Notice of the Supplemental Indenture was provided to the holders of the 2019 Notes on March 8, 2018 in accordance with Section 9.04 of the Indenture. We believe the allegations are completely without merit, reject all claims raised by the plaintiffs and intend to vigorously defend this matter.

In November 2017, CyDex, our wholly owned subsidiary, received a paragraph IV certification from Teva Pharmaceuticals USA, Inc., Teva Pharmaceutical Industries Ltd. and Actavis, LLC (collectively “Teva”) alleging that certain of our patents related to Captisol were invalid, unenforceable and/or will not be infringed by Teva’s ANDA related to Spectrum Pharmaceuticals’ NDA for Evomela. On December 20, 2017, CyDex filed a complaint against Teva in the U.S. District Court for the District of Delaware, asserting that Teva’s ANDA would infringe our patents. On March 22, Teva filed an answer and counterclaims seeking declarations of non-infringement and invalidity as to each of the asserted patents and on April 12, CyDex filed an answer to Teva’s counterclaims.