Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements and Marketable Securities - Summary of Company's Available-for-Sale Securities (Detail)

v2.4.1.9
Fair Value Measurements and Marketable Securities - Summary of Company's Available-for-Sale Securities (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis $ 62,038us-gaap_AvailableForSaleSecuritiesAmortizedCost $ 50,222us-gaap_AvailableForSaleSecuritiesAmortizedCost
Unrealized Gain 6us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax 4us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Unrealized Loss (21)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax (17)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Fair Value 62,023us-gaap_AvailableForSaleSecurities 50,209us-gaap_AvailableForSaleSecurities
Money Market Funds    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 10,366us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_MoneyMarketFundsMember
3,369us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_MoneyMarketFundsMember
Unrealized Gain 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_MoneyMarketFundsMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_MoneyMarketFundsMember
Unrealized Loss 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_MoneyMarketFundsMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_MoneyMarketFundsMember
Fair Value 10,366us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_MoneyMarketFundsMember
3,369us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_MoneyMarketFundsMember
Certificates of Deposit    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 1,475us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CertificatesOfDepositMember
2,505us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CertificatesOfDepositMember
Unrealized Gain 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CertificatesOfDepositMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CertificatesOfDepositMember
Unrealized Loss 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CertificatesOfDepositMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CertificatesOfDepositMember
Fair Value 1,475us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CertificatesOfDepositMember
2,505us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CertificatesOfDepositMember
Corporate Debt Securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 31,950us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
28,094us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Unrealized Gain 4us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
1us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Unrealized Loss (19)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
(14)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Fair Value 31,935us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
28,081us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
U.S. Government Securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 24,021us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USGovernmentDebtSecuritiesMember
19,123us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USGovernmentDebtSecuritiesMember
Unrealized Gain 2us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USGovernmentDebtSecuritiesMember
3us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USGovernmentDebtSecuritiesMember
Unrealized Loss (2)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USGovernmentDebtSecuritiesMember
(3)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USGovernmentDebtSecuritiesMember
Fair Value 24,021us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USGovernmentDebtSecuritiesMember
19,123us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USGovernmentDebtSecuritiesMember
Commercial Paper    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 14,240us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
5,499us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
Unrealized Gain 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
Unrealized Loss 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
Fair Value 14,240us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
5,499us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
Marketable Securities Including Cash Equivalents    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 82,052us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= thld_MarketableSecuritiesIncludingCashEquivalentsMember
58,590us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= thld_MarketableSecuritiesIncludingCashEquivalentsMember
Unrealized Gain 6us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= thld_MarketableSecuritiesIncludingCashEquivalentsMember
4us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= thld_MarketableSecuritiesIncludingCashEquivalentsMember
Unrealized Loss (21)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= thld_MarketableSecuritiesIncludingCashEquivalentsMember
(17)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= thld_MarketableSecuritiesIncludingCashEquivalentsMember
Fair Value 82,037us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= thld_MarketableSecuritiesIncludingCashEquivalentsMember
58,577us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= thld_MarketableSecuritiesIncludingCashEquivalentsMember
Less Cash Equivalents    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 20,014us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CashEquivalentsMember
8,368us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CashEquivalentsMember
Unrealized Gain 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CashEquivalentsMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CashEquivalentsMember
Unrealized Loss 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CashEquivalentsMember
0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CashEquivalentsMember
Fair Value $ 20,014us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CashEquivalentsMember
$ 8,368us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CashEquivalentsMember