Basis of presentation, principles of consolidation and significant accounting policies - Impact of Topic 606 Adoption on Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Basis Of Presentation And Significant Accounting Policies [Line Items]
Deferred revenue, current portion	$ 34,040	$ 45,344	$ 25,674
Deferred revenue, net of current portion	28,806	31,468	21,763
Accumulated deficit	(1,058,308)	(943,183)	$ (913,808)
ASU 2014-09 [Member] \| Adjustments [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Deferred revenue, current portion	14,503	19,670
Deferred revenue, net of current portion	8,740	9,705
Accumulated deficit	(23,243)	(29,375)
ASU 2014-09 [Member] \| Balances Without Adoption of Topic 606 [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Deferred revenue, current portion	19,537	25,674
Deferred revenue, net of current portion	20,066	21,763
Accumulated deficit	$ (1,035,065)	$ (913,808)

The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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