Discontinued operations - Schedule of Gain (Loss) on Disposal Activity (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)
Loss On Disposal Of Discontinued Operations [Line Items]
Write off of unamortized debt costs	$ 284
Spin-off Red Violet
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) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

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