Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Uncertain tax positions	$ 0	$ 0
Minimum [Member]
Income Tax Contingency [Line Items]
Distribution of taxable income to qualify as REIT, percent	90.00%

Amount recognized for uncertainty in income taxes classified as current.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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