Assets Held for Sale or Contribution - Summary of Assets Held for Sale or Contribution (Detail) ft² in Thousands, $ in Thousands	Dec. 31, 2018 USD ($) ft² Property	Dec. 31, 2017 USD ($) ft² Property
Long Lived Assets Held For Sale [Line Items]
Total assets held for sale or contribution	$ 622,288	$ 342,060
Total liabilities associated with assets held for sale or contribution – included in Other Liabilities	$ 12,972	$ 9,341
Disposal Group Held for Sale Not Discontinued Operations
Long Lived Assets Held For Sale [Line Items]
Number of operating properties \| Property	57	22
Square feet \| ft²	8,236	5,384

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

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