Basis of presentation, principles of consolidation and significant accounting policies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) Segment	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Basis Of Presentation And Significant Accounting Policies [Line Items]
Number of operating segment | Segment	1
Operating lease liabilities	$ 185,766	$ 125,800
Operating lease right-of-use assets	184,618	$ 127,300
Financing lease obligation, current portion			$ 1,424
ASU 2016-02 [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Increase to deferred tax assets	5,300
Increase to deferred tax liabilities	7,100
Net increase to deferred tax liabilities	1,800
ASU 2016-02 [Member] | 60 Binney Street [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Operating lease liabilities	177,000
Operating lease right-of-use assets	184,400
Financing lease obligation	149,300
Financing lease obligation, current portion	1,400
Financing lease obligation, net of current portion	153,300
Adjustment on accumulated deficit	$ 6,600