Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($)
Accounting Standards Update No. 2017-01 [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Decrease normalized funds from operations	$ (1)
Accounting Standards Update No. 2017-01 [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Decrease normalized funds from operations	(2)
Accounting Standards Update 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings	$ 2

Amount of the effect of a change in accounting principle on operating profit or loss.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22499-107794

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22580-107794

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22583-107794

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration