Discontinued operations - Schedule of Gain (Loss) on Disposal Activity (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($)
Loss On Disposal Of Discontinued Operations [Line Items]
Loss on disposal of discontinued operations	$ (19,040)
Discontinued Operations, Disposed of [Member]
Loss On Disposal Of Discontinued Operations [Line Items]
Share-based compensation expense	15,548
Write-off of unamortized debt costs	284
Write-off of certain prepaid expenses	198
Spin-off related professional fees	2,012
Spin-off related employee compensation	998
Loss on disposal of discontinued operations	$ 19,040

Amount before tax of gain (loss) not previously recognized resulting from the disposal of a discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721525-107759

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1361-107760

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=65878427&loc=d3e957-107759

Name:	us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration