Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation (Investment Categories) (Details)

v2.4.1.9
Basis of Presentation (Investment Categories) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Summary of investment categories    
Cost $ 2,725us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis $ 3,440us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Gross unrealized gains 9,334us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax 4,954us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Gross unrealized losses 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Estimated fair value 12,059us-gaap_AvailableForSaleSecuritiesDebtSecurities 8,394us-gaap_AvailableForSaleSecuritiesDebtSecurities
Short-term investments    
Summary of investment categories    
Cost 2,125us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
2,179us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
Gross unrealized gains 9,334us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
4,954us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
Gross unrealized losses 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
Estimated fair value 11,459us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
7,133us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
Certificates of deposit-restricted    
Summary of investment categories    
Cost 600us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= lgnd_CertificatesOfDepositRestrictedMember
1,261us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_InvestmentTypeAxis
= lgnd_CertificatesOfDepositRestrictedMember
Gross unrealized gains 0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= lgnd_CertificatesOfDepositRestrictedMember
0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= lgnd_CertificatesOfDepositRestrictedMember
Gross unrealized losses 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= lgnd_CertificatesOfDepositRestrictedMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= lgnd_CertificatesOfDepositRestrictedMember
Estimated fair value $ 600us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= lgnd_CertificatesOfDepositRestrictedMember
$ 1,261us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_InvestmentTypeAxis
= lgnd_CertificatesOfDepositRestrictedMember