Basis of presentation, principles of consolidation and significant accounting policies - Impact of Topic 606 Adoption on Condensed Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Basis Of Presentation And Significant Accounting Policies [Line Items]
Net loss	$ (115,126)	$ (68,712)
Changes in deferred revenue	(13,966)	$ (3,969)
ASU 2014-09 [Member] | Adjustments [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Net loss	6,133
Changes in deferred revenue	(6,133)
ASU 2014-09 [Member] | Balances Without Adoption of Topic 606 [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Net loss	(121,259)
Changes in deferred revenue	$ (7,833)