Commitments and contingencies	3 Months Ended
Mar. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and contingencies	7. Commitments and contingencies The Company is party to various agreements, principally relating to licensed technology, that require future payments relating to milestones not met at March 31, 2016 and December 31, 2015 or royalties on future sales of specified products. The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to these agreements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners or customers, in connection with claims by any third party with respect to the Company’s products or business activities. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements. The Company’s wholly-owned subsidiary bluebird bio France – SARL participates in the French Crédit d’Impôt Recherche (“CIR”) program, which allows companies to monetize up to 30% of eligible research expenses. The Company received aggregate reimbursement of €1.6 million related to years 2012 through 2014. The Company has applied for €1.0 million related to the year ended December 31, 2015, and has not yet applied for the €0.4 million related to the three months ended March 31, 2016. The €1.0 million is classified as a short term receivable within the condensed consolidated balance sheets as of March 31, 2016. The years 2012 through 2016 are open and subject to examination. Operating Lease Commitments On June 3, 2013, the Company entered into a nine-year building lease for approximately 43,600 square feet of space located at 150 Second Street, Cambridge, Massachusetts, which commenced in December 2013. This lease was amended in June 2014 to add approximately 9,900 square feet. The lease originally had monthly lease payments of $0.2 million for the first 12 months, which increased to $0.3 million per month beginning in December 2014 due to the lease amendment, with annual rent escalations thereafter. Rent expense is recognized on a straight-line basis over the term of the lease. The Company has the option to extend this lease by an additional five years. The lease provided a contribution from the landlord towards the initial build-out of the space of up to $7.8 million. The Company capitalizes the leasehold improvements as property and equipment and records the landlord incentive payments received as deferred rent and amortizes these amounts as reductions to rent expense over the lease term. In addition, in accordance with the lease, the Company entered into a cash-collateralized irrevocable standby letter of credit in the amount of $1.3 million, naming the landlord as beneficiary. This may be reduced to $0.6 million upon the second anniversary of the rent commencement date in the second quarter of 2016. On June 29, 2015, the Company entered into a lease agreement for additional office space located at 215 First Street, Cambridge, Massachusetts. Under the terms of the lease, the Company leased approximately 15,120 square feet starting on July 13, 2015 for $0.5 million per year in base rent, which is subject to a 3% annual rent increase plus certain operating expenses and taxes. The lease will continue until the end of the 60^th full calendar month following the date the landlord delivers the premises to the Company, and includes early termination provisions that could allow the Company to terminate the lease at the end of the 20^th full calendar month following the delivery of the premises if the Company meets certain conditions specified within the lease. Under the terms of the lease, the Company has also leased an additional 8,075 square feet of office space in the same premises starting on January 1, 2016 for an additional $0.3 million per year in base rent, which is subject to a 3% annual rent increase plus certain operating expenses and taxes. 60 Binney Street Lease Commitments On September 21, 2015, the Company entered into a lease agreement for additional office and laboratory space located in a building (the “Building”) under construction at 60 Binney Street, Cambridge, Massachusetts (the “60 Binney Lease”). Under the terms of the 60 Binney Lease, starting on October 1, 2016, the Company will lease approximately 253,108 square feet of office and laboratory space at $72.50 per square foot per year, or $18.4 million per year in base rent, which is subject to scheduled annual rent increases of 1.75% plus certain operating expenses and taxes. The Company also executed a $9.2 million letter of credit upon signing the 60 Binney Lease, which was required to be collateralized with a bank account at a financial institution in accordance with the 60 Binney Lease agreement. This $9.2 million is subject to increase to $13.8 million when the Company first requests reimbursement of tenant improvement costs from the landlord. Subject to the terms of the lease and certain reduction requirements specified therein, including market capitalization requirements, this amount may decrease back to $9.2 million over time. The 60 Binney Lease will continue until the end of the 120^th full calendar month following April 2017 or the earlier the date the Company occupies the Building or other conditions specified in the 60 Binney Lease occur. Pursuant to a work letter entered into in connection with the 60 Binney Lease, the landlord will contribute an aggregate of $42.4 million toward the cost of construction and tenant improvements for the Building. The purpose of the 60 Binney Lease is to supplement and eventually replace the Company’s current leased premises at 150 Second Street and 215 First Street in Cambridge, Massachusetts and the Company intends to move its corporate headquarters to 60 Binney Street in mid-2017. The Company has the option to extend the 60 Binney Lease for two successive five-year terms. Because the Company is involved in the construction project, including having responsibility to pay for a portion of the costs of finish work and mechanical, electrical, and plumbing elements of the Building, the Company is deemed for accounting purposes to be the owner of the Building during the construction period. Accordingly, the Company has recorded project construction costs incurred by the landlord as an asset in “Property and equipment, net” and a related financing obligation in “Construction financing lease obligation” on the Company’s condensed consolidated balance sheet. The Company bifurcates its future lease payments pursuant to the 60 Binney Lease into (i) a portion that is allocated to the Building and (ii) a portion that is allocated to the land on which the Building is being constructed, which is recorded as rental expense. Although the Company estimates that the Company will not begin making lease payments pursuant to the 60 Binney Lease until April 2017, the portion of the lease obligation allocated to the land is treated for accounting purposes as an operating lease that commenced upon execution of the 60 Binney Lease in September 2015. During the three months ended March 31, 2016, the Company recognized $0.5 million of non-cash rental expense attributable to the land. As of March 31, 2016, Property and equipment, net, includes $74.7 million related to construction costs for the Building. The construction financing lease obligation related to the Building was $74.4 million. No cash has been paid to the landlord to date. Once the landlord completes the construction of the Building, the Company will evaluate the 60 Binney Lease in order to determine whether or not the 60 Binney Lease meets the criteria for “sale-leaseback” treatment. If the 60 Binney Lease meets the “sale-leaseback” criteria, the Company will remove the asset and the related liability from its consolidated balance sheet and treat the 60 Binney Lease as either an operating or a capital lease based on the Company’s assessment of the accounting guidance. The Company expects that upon completion of construction of the Building the 60 Binney Lease will not meet the “sale-leaseback” criteria. If the 60 Binney Lease does not meet “sale-leaseback” criteria, the Company will treat the 60 Binney Lease as a financing obligation and will depreciate the asset in accordance with the Company’s accounting policy.

7. Commitments and contingencies

The Company is party to various agreements, principally relating to licensed technology, that require future payments relating to milestones not met at March 31, 2016 and December 31, 2015 or royalties on future sales of specified products.

The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to these agreements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners or customers, in connection with claims by any third party with respect to the Company’s products or business activities. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements.

The Company’s wholly-owned subsidiary bluebird bio France – SARL participates in the French Crédit d’Impôt Recherche (“CIR”) program, which allows companies to monetize up to 30% of eligible research expenses. The Company received aggregate reimbursement of €1.6 million related to years 2012 through 2014. The Company has applied for €1.0 million related to the year ended December 31, 2015, and has not yet applied for the €0.4 million related to the three months ended March 31, 2016. The €1.0 million is classified as a short term receivable within the condensed consolidated balance sheets as of March 31, 2016. The years 2012 through 2016 are open and subject to examination.

Operating Lease Commitments

On June 3, 2013, the Company entered into a nine-year building lease for approximately 43,600 square feet of space located at 150 Second Street, Cambridge, Massachusetts, which commenced in December 2013. This lease was amended in June 2014 to add approximately 9,900 square feet. The lease originally had monthly lease payments of $0.2 million for the first 12 months, which increased to $0.3 million per month beginning in December 2014 due to the lease amendment, with annual rent escalations thereafter. Rent expense is recognized on a straight-line basis over the term of the lease. The Company has the option to extend this lease by an additional five years. The lease provided a contribution from the landlord towards the initial build-out of the space of up to $7.8 million. The Company capitalizes the leasehold improvements as property and equipment and records the landlord incentive payments received as deferred rent and amortizes these amounts as reductions to rent expense over the lease term. In addition, in accordance with the lease, the Company entered into a cash-collateralized irrevocable standby letter of credit in the amount of $1.3 million, naming the landlord as beneficiary. This may be reduced to $0.6 million upon the second anniversary of the rent commencement date in the second quarter of 2016.

On June 29, 2015, the Company entered into a lease agreement for additional office space located at 215 First Street, Cambridge, Massachusetts. Under the terms of the lease, the Company leased approximately 15,120 square feet starting on July 13, 2015 for $0.5 million per year in base rent, which is subject to a 3% annual rent increase plus certain operating expenses and taxes. The lease will continue until the end of the 60^th full calendar month following the date the landlord delivers the premises to the Company, and includes early termination provisions that could allow the Company to terminate the lease at the end of the 20^th full calendar month following the delivery of the premises if the Company meets certain conditions specified within the lease. Under the terms of the lease, the Company has also leased an additional 8,075 square feet of office space in the same premises starting on January 1, 2016 for an additional $0.3 million per year in base rent, which is subject to a 3% annual rent increase plus certain operating expenses and taxes.

60 Binney Street Lease Commitments

On September 21, 2015, the Company entered into a lease agreement for additional office and laboratory space located in a building (the “Building”) under construction at 60 Binney Street, Cambridge, Massachusetts (the “60 Binney Lease”). Under the terms of the 60 Binney Lease, starting on October 1, 2016, the Company will lease approximately 253,108 square feet of office and laboratory space at $72.50 per square foot per year, or $18.4 million per year in base rent, which is subject to scheduled annual rent increases of 1.75% plus certain operating expenses and taxes. The Company also executed a $9.2 million letter of credit upon signing the 60 Binney Lease, which was required to be collateralized with a bank account at a financial institution in accordance with the 60 Binney Lease agreement. This $9.2 million is subject to increase to $13.8 million when the Company first requests reimbursement of tenant improvement costs from the landlord. Subject to the terms of the lease and certain reduction requirements specified therein, including market capitalization requirements, this amount may decrease back to $9.2 million over time. The 60 Binney Lease will continue until the end of the 120^th full calendar month following April 2017 or the earlier the date the Company occupies the Building or other conditions specified in the 60 Binney Lease occur. Pursuant to a work letter entered into in connection with the 60 Binney Lease, the landlord will contribute an aggregate of $42.4 million toward the cost of construction and tenant improvements for the Building. The purpose of the 60 Binney Lease is to supplement and eventually replace the Company’s current leased premises at 150 Second Street and 215 First Street in Cambridge, Massachusetts and the Company intends to move its corporate headquarters to 60 Binney Street in mid-2017. The Company has the option to extend the 60 Binney Lease for two successive five-year terms.

Because the Company is involved in the construction project, including having responsibility to pay for a portion of the costs of finish work and mechanical, electrical, and plumbing elements of the Building, the Company is deemed for accounting purposes to be the owner of the Building during the construction period. Accordingly, the Company has recorded project construction costs incurred by the landlord as an asset in “Property and equipment, net” and a related financing obligation in “Construction financing lease obligation” on the Company’s condensed consolidated balance sheet.

The Company bifurcates its future lease payments pursuant to the 60 Binney Lease into (i) a portion that is allocated to the Building and (ii) a portion that is allocated to the land on which the Building is being constructed, which is recorded as rental expense. Although the Company estimates that the Company will not begin making lease payments pursuant to the 60 Binney Lease until April 2017, the portion of the lease obligation allocated to the land is treated for accounting purposes as an operating lease that commenced upon execution of the 60 Binney Lease in September 2015. During the three months ended March 31, 2016, the Company recognized $0.5 million of non-cash rental expense attributable to the land.

As of March 31, 2016, Property and equipment, net, includes $74.7 million related to construction costs for the Building. The construction financing lease obligation related to the Building was $74.4 million. No cash has been paid to the landlord to date.

Once the landlord completes the construction of the Building, the Company will evaluate the 60 Binney Lease in order to determine whether or not the 60 Binney Lease meets the criteria for “sale-leaseback” treatment. If the 60 Binney Lease meets the “sale-leaseback” criteria, the Company will remove the asset and the related liability from its consolidated balance sheet and treat the 60 Binney Lease as either an operating or a capital lease based on the Company’s assessment of the accounting guidance. The Company expects that upon completion of construction of the Building the 60 Binney Lease will not meet the “sale-leaseback” criteria. If the 60 Binney Lease does not meet “sale-leaseback” criteria, the Company will treat the 60 Binney Lease as a financing obligation and will depreciate the asset in accordance with the Company’s accounting policy.