Pro Forma Consolidated Financial Information - Additional Information (Detail) - USD ($)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Business Acquisition Pro Forma Information [Abstract]
Pro forma acquisition related expenses	$ 0	$ 2,600,000

Asset acquisition proforma acquisition related costs.

No definition available.

Name:	ck0001698538_AssetAcquisitionProformaAcquisitionRelatedCosts
Namespace Prefix:	ck0001698538_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration