Fair Value of Financial Instruments	12 Months Ended
Dec. 31, 2014
Fair Value of Financial Instruments	11. Fair Value of Financial Instruments The Company provides disclosure of financial assets and financial liabilities that are carried at fair value based on the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements may be classified based on the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities using the following three levels: Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.) and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs). Level 3—Unobservable inputs that reflect the Company’s estimates of the assumptions that market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available, including its own data. As of December 31, 2014 and 2013, the Company did not hold any assets recorded at fair value. At December 31, 2014 and 2013, the carrying amounts of cash equivalents, accounts payable and accrued liabilities approximate fair value because of their short-term nature. The carrying amount of the Company’s bank term loan at December 31, 2013 approximated fair value due to its variable interest rate and other terms. All such measurements are Level 2 measurements in the fair value hierarchy. The carrying amount of the Company’s leased buildings under construction in Cambridge, Massachusetts and the related long term facility lease obligation reflect replacement cost, which approximates fair value. This measurement is a Level 3 fair value measurement. The fair value of the convertible notes, which differs from their carrying value, is influenced by interest rates and stock price and stock price volatility and is determined by prices for the convertible notes observed in market trading. The market for trading of the convertible notes is not considered to be an active market and therefore the estimate of fair value is based on Level 2 inputs. The estimated fair value of the convertible notes, face value of $200 million, was $203.4 million at December 31, 2014.

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2014

11. Fair Value of Financial Instruments

The Company provides disclosure of financial assets and financial liabilities that are carried at fair value based on the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements may be classified based on the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities using the following three levels:

Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level 2—Inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.) and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs).

Level 3—Unobservable inputs that reflect the Company’s estimates of the assumptions that market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available, including its own data.

As of December 31, 2014 and 2013, the Company did not hold any assets recorded at fair value.

At December 31, 2014 and 2013, the carrying amounts of cash equivalents, accounts payable and accrued liabilities approximate fair value because of their short-term nature. The carrying amount of the Company’s bank term loan at December 31, 2013 approximated fair value due to its variable interest rate and other terms. All such measurements are Level 2 measurements in the fair value hierarchy. The carrying amount of the Company’s leased buildings under construction in Cambridge, Massachusetts and the related long term facility lease obligation reflect replacement cost, which approximates fair value. This measurement is a Level 3 fair value measurement. The fair value of the convertible notes, which differs from their carrying value, is influenced by interest rates and stock price and stock price volatility and is determined by prices for the convertible notes observed in market trading. The market for trading of the convertible notes is not considered to be an active market and therefore the estimate of fair value is based on Level 2 inputs. The estimated fair value of the convertible notes, face value of $200 million, was $203.4 million at December 31, 2014.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References+ Details