Investments in real estate properties are presented at cost, and consist of the following as of December 31 (square feet and dollars in thousands):
| Square Feet /Acres (1) | No. of Buildings (1) | Investment Balance | ||||||||||||||||||||||
| 2013 | 2012 | 2013 | 2012 | 2013 | 2012 | |||||||||||||||||||
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Industrial operating properties: |
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Improved land |
- - | - - | - - | - - | $ | 4,074,647 | $ | 5,317,123 | ||||||||||||||||
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Buildings and improvements |
267,097 | 316,347 | 1,610 | 1,853 | 13,726,417 | 17,291,125 | ||||||||||||||||||
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Development portfolio, including cost of land: |
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Pre-stabilized |
4,491 | 4,785 | 11 | 15 | 204,022 | 472,413 | ||||||||||||||||||
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Properties under development |
18,587 | 13,216 | 46 | 30 | 816,995 | 479,230 | ||||||||||||||||||
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Land |
9,747 | 10,915 | - - | - - | 1,516,166 | 1,794,364 | ||||||||||||||||||
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Other real estate investments (2) |
- - | - - | - - | - - | 486,230 | 454,868 | ||||||||||||||||||
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Total investments in real estate properties |
20,824,477 | 25,809,123 | ||||||||||||||||||||||
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Less accumulated depreciation |
2,568,998 | 2,480,660 | ||||||||||||||||||||||
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Net investments in real estate properties |
$ | 18,255,479 | $ | 23,328,463 | ||||||||||||||||||||
| (1) | Items indicated by ‘ - - ‘ are not applicable. |
| (2) | Included in other investments were: (i) certain non-industrial real estate; (ii) our corporate office buildings; (iii) land parcels that are ground leased to third parties; (iv) certain infrastructure costs related to projects we are developing on behalf of others; (v) costs related to future development projects, including purchase options on land; (vi) earnest money deposits associated with potential acquisitions; and (vii) restricted funds that are held in escrow pending the completion of tax-deferred exchange transactions involving operating properties. |