Annual report pursuant to Section 13 and 15(d)

Collaboration Arrangements - Additional Information (Detail)

v2.4.1.9
Collaboration Arrangements - Additional Information (Detail) (Merck KGaA, USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended 35 Months Ended
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2014
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]          
Upfront and milestone payments received to date $ 12.5us-gaap_ProceedsFromCollaborators $ 110.0us-gaap_ProceedsFromCollaborators     $ 110.0us-gaap_ProceedsFromCollaborators
Merck KGaA's percentage share of worldwide development expenses   70.00%thld_WorldwideDevelopmentExpensesSharePercentage      
Collaboration payments achieved and received     42.5thld_CollaborationPayments 67.5thld_CollaborationPayments  
Revenue recognized by the Company   14.7us-gaap_DeferredRevenueRevenueRecognized 12.5us-gaap_DeferredRevenueRevenueRecognized 5.9us-gaap_DeferredRevenueRevenueRecognized  
Company earned a reimbursement for eligible worldwide development expenses   21.9us-gaap_RecoveryOfDirectCosts 16.5us-gaap_RecoveryOfDirectCosts 13.1us-gaap_RecoveryOfDirectCosts  
United States
         
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]          
Portion of profits that Company is eligible to participate, depending upon total sales   50.00%thld_PortionOfProfitsDependingOnSales
/ dei_LegalEntityAxis
= thld_MerckKGaAMember
/ us-gaap_StatementGeographicalAxis
= country_US
     
Regulatory and Development Milestones | Maximum
         
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]          
Potential future milestones   100thld_PotentialMilestonePayments
/ dei_LegalEntityAxis
= thld_MerckKGaAMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ thld_RequirementOfEligibleFutureMilestonePaymentsAxis
= thld_RegulatoryAndDevelopmentMilestonesMember
     
Commercialization Milestones | Maximum
         
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]          
Potential future milestones   $ 340thld_PotentialMilestonePayments
/ dei_LegalEntityAxis
= thld_MerckKGaAMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ thld_RequirementOfEligibleFutureMilestonePaymentsAxis
= thld_CommercializationMilestonesMember