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Stockholders' Equity (Details) (USD $)
3 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Share-Based Compensation      
Stock-based compensation expense $ 722,000us-gaap_AllocatedShareBasedCompensationExpense $ 239,000us-gaap_AllocatedShareBasedCompensationExpense  
Employee Stock Purchase Plan      
Share-Based Compensation      
Shares available for grant 220,588us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember
   
Percentage of full share price paid in purchase of common stock 85.00ttoo_PercentageOfFullSharePricePaidInPurchaseOfCommonStock
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember
   
Maximum amount of annual employee common stock purchases 25,000ttoo_MaximumAmountOfAnnualEmployeeCommonStockPurchases
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember
   
Stock-based compensation expense 60,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember
   
2006 and 2014 Stock Option Plans | Stock Options      
Share-Based Compensation      
Aggregate fair value of options granted 5,000,000ttoo_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodTotalGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Number of Shares      
Outstanding, beginning of the period (in shares) 2,911,146us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Granted (in shares) 516,954us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Exercised (in shares) (157,324)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Cancelled (in shares) (46,724)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Outstanding, end of the period (in shares) 3,224,052us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
  2,911,146us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
Exercisable (in shares) 1,543,881us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Vested or expected to vest (in shares) 2,827,095us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Weighted Average Exercise Price Per Share      
Outstanding, beginning of the period (in dollars per share) $ 5.30us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Granted (in dollars per share) $ 18.20us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Exercised (in dollars per share) $ 2.38us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Cancelled (in dollars per share $ 7.97us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Outstanding, end of the period (in dollars per share) $ 7.47us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
  $ 5.30us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
Exercisable (in dollars per share) $ 2.74us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Vested or expected to vest (in dollars per share) $ 7.09us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Weighted-Average Remaining Contractual Term (in years)      
Outstanding, beginning of the period (in years) 8 years 11 days   7 years 10 months 13 days
Outstanding, end of the period (in years) 8 years 11 days   7 years 10 months 13 days
Exercisable (in years) 6 years 6 months 22 days    
Vested or expected to vest (in years) 7 years 10 months 21 days    
Aggregate Intrinsic Value      
Outstanding, beginning of the period 40,586,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Exercised 2,067,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Outstanding, end of the period 25,954,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
  40,586,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
Exercisable 19,733,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Vested or expected to vest 23,822,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
   
Fair value assumptions      
Weighted average fair value of options granted (in dollars per share) $ 9.75us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
$ 5.73us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
 
Weighted-average risk-free interest rate 1.70%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
2.04%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
 
Expected dividend yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
 
Expected volatility 56.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
62.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
 
Expected terms 6 years 1 month 6 days 6 years 1 month 6 days  
Fair value of stock options vested $ 499,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
$ 137,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlans2006And2014Member
 
2014 Stock Option Plan | Stock Options      
Share-Based Compensation      
Common stock were reserved for issuance 823,529us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlan2014Member
   
Shares available for grant 878,282us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlan2014Member
   
Percentage of common shares outstanding 4.00%ttoo_PercentageOfCommonSharesOutstanding
/ us-gaap_AwardTypeAxis
= ttoo_EmployeeAndNonEmployeeStockOptionsMember
/ us-gaap_PlanNameAxis
= ttoo_StockOptionPlan2014Member
   
2014 Stock Option Plan | Maximum | Stock Options      
Share-Based Compensation      
Expiration Period 10 years    
Vesting period 4 years    
2006 Stock Option Plan | Maximum | Stock Options      
Share-Based Compensation      
Expiration Period 10 years    
Vesting period 4 years