Discontinued operations - Schedule of Gain (Loss) on Disposal Activity (Detail) $ in Thousands	6 Months Ended
Jun. 30, 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109222650&loc=d3e1361-107760

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=109222160&loc=SL51721525-107759

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