Commitments and contingencies - Future Minimum Commitments (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Future Minimum Payments Due [Line Items]
2017	$ 26,424
2018	29,015
2019	28,815
2020	29,146
2021	29,484
2022 and thereafter	141,600
Total minimum lease payments	284,484
Other Operating Lease [Member]
Future Minimum Payments Due [Line Items]
2017	11,963
2018	10,368
2019	9,841
2020	9,841
2021	9,841
2022 and thereafter	32,725
Total minimum lease payments	84,579
150 Second Street Lease [Member]
Future Minimum Payments Due [Line Items]
2017	1,359
Total minimum lease payments	1,359
60 Binney Street Lease [Member]
Future Minimum Payments Due [Line Items]
2017	13,102
2018	18,647
2019	18,974
2020	19,305
2021	19,643
2022 and thereafter	108,875
Total minimum lease payments	$ 198,546