Subsequent events	3 Months Ended
Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent events	14. Subsequent events In April 2019, the Company entered into a sublease agreement for office space located at 50 Binney Street in Cambridge, Massachusetts (the “50 Binney Street Sublease”) to supplement the Company’s corporate headquarters located at 60 Binney Street in Cambridge, Massachusetts. Under the terms of the 50 Binney Street Sublease, the Company will lease 267,278 square feet of office space for $99.95 per square foot, or $26.7 million per year in base rent subject to certain operating expenses, taxes and annual rent increases. The Company anticipates the lease will commence on July 1, 2021 and end on December 31, 2030, unless the Company earlier occupies the premises or other conditions specified in the 50 Binney Street Sublease occur. The sublessor has the right to postpone the commencement date until January 1, 2022 by providing not less than nine months’ prior written notice to the Company. Upon signing the 50 Binney Street Sublease, the Company executed a $40.1 million cash-collateralized letter of credit, which may be reduced in the future subject to the terms of the 50 Binney Street Sublease and certain reduction requirements specified therein. Payments will commence at the earlier of (i) the date which is 90 days following the commencement date and (ii) the date the Company takes occupancy of all or any portion of the premises.

Subsequent events

3 Months Ended

Mar. 31, 2019

14. Subsequent events

In April 2019, the Company entered into a sublease agreement for office space located at 50 Binney Street in Cambridge, Massachusetts (the “50 Binney Street Sublease”) to supplement the Company’s corporate headquarters located at 60 Binney Street in Cambridge, Massachusetts. Under the terms of the 50 Binney Street Sublease, the Company will lease 267,278 square feet of office space for $99.95 per square foot, or $26.7 million per year in base rent subject to certain operating expenses, taxes and annual rent increases. The Company anticipates the lease will commence on July 1, 2021 and end on December 31, 2030, unless the Company earlier occupies the premises or other conditions specified in the 50 Binney Street Sublease occur. The sublessor has the right to postpone the commencement date until January 1, 2022 by providing not less than nine months’ prior written notice to the Company. Upon signing the 50 Binney Street Sublease, the Company executed a $40.1 million cash-collateralized letter of credit, which may be reduced in the future subject to the terms of the 50 Binney Street Sublease and certain reduction requirements specified therein. Payments will commence at the earlier of (i) the date which is 90 days following the commencement date and (ii) the date the Company takes occupancy of all or any portion of the premises.