Discontinued operations - Schedule of Gain (Loss) on Disposal Activity (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018
Loss On Disposal Of Discontinued Operations [Line Items]
Loss on disposal of discontinued operations		$ (19,040)
Discontinued Operations, Disposed of
Loss On Disposal Of Discontinued Operations [Line Items]
Share-based compensation expense	$ 0	15,548
Write-off of unamortized debt costs	0	284
Write-off of certain prepaid expenses	0	198
Spin-off related professional fees	0	2,012
Spin-off related employee compensation	0	998
Loss on disposal of discontinued operations	$ 0	$ 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
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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