Assets Held for Sale or Contribution - Summary of Assets Held for Sale or Contribution (Detail) ft² in Thousands, $ in Thousands	Dec. 31, 2017 USD ($) ft² Property	Dec. 31, 2016 USD ($) ft² Property
Long Lived Assets Held For Sale [Line Items]
Total assets held for sale or contribution	$ 342,060	$ 322,139
Total liabilities associated with assets held for sale or contribution – included in Other Liabilities	$ 9,341	$ 4,984
Disposal Group Heldforsale Not Discontinued Operations
Long Lived Assets Held For Sale [Line Items]
Number of operating properties \| Property	22	13
Square feet \| ft²	5,384	4,167

Amount classified as liabilities attributable to disposal group held for sale or disposed of.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2941-110230

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=65878427&loc=d3e1107-107759

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721533-107759

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721673-107760

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