| Schedule of operating properties, net | 
Operating properties, net consisted of the following (in thousands):  
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   | 
December 31,  | 
 
   | 
2017  | 
   | 
2016  | 
 
Land  | 
$  | 
455,680  | 
 
  | 
   | 
$  | 
433,311  | 
 
  | 
 
Buildings and improvements  | 
3,068,124  | 
 
  | 
   | 
2,944,905  | 
 
  | 
 
Less: Accumulated depreciation  | 
(786,193  | 
)  | 
   | 
(706,385  | 
)  | 
 
Operating properties, net  | 
$  | 
2,737,611  | 
 
  | 
   | 
$  | 
2,671,831  | 
 
  | 
 
  
 
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| Schedule of operating property dispositions | 
In 2017, we sold the following operating properties (dollars in thousands): 
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Project Name  | 
   | 
City, State  | 
   | 
Segment  | 
   | 
Date of Sale  | 
   | 
Number of Buildings  | 
   | 
Total Rentable Square Feet  | 
   | 
Transaction Value  | 
   | 
Gain on Sale  | 
 
3120 Fairview Park Drive  | 
   | 
Falls Church, VA  | 
   | 
Northern Virginia Defense/IT   | 
   | 
2/15/2017  | 
   | 
1  | 
 
  | 
   | 
190,000  | 
 
  | 
   | 
$  | 
39,000  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
 
1334 Ashton Road  | 
   | 
Hanover, MD  | 
   | 
Fort Meade/BW Corridor  | 
   | 
6/9/2017  | 
   | 
1  | 
 
  | 
   | 
37,000  | 
 
  | 
   | 
2,300  | 
 
  | 
   | 
—  | 
 
  | 
 
Remaining White Marsh Properties (1)  | 
   | 
White Marsh, MD  | 
   | 
Regional Office and Other  | 
   | 
7/28/2017  | 
   | 
8  | 
 
  | 
   | 
412,000  | 
 
  | 
   | 
47,500  | 
 
  | 
   | 
1,180  | 
 
  | 
 
201 Technology Drive  | 
   | 
Lebanon, VA  | 
   | 
Data Center Shells  | 
   | 
10/27/2017  | 
   | 
1  | 
 
  | 
   | 
103,000  | 
 
  | 
   | 
29,500  | 
 
  | 
   | 
3,625  | 
 
  | 
 
7320 Parkway Drive  | 
   | 
Hanover, MD  | 
   | 
Fort Meade/BW Corridor  | 
   | 
12/15/2017  | 
   | 
1  | 
 
  | 
   | 
57,000  | 
 
  | 
   | 
7,529  | 
 
  | 
   | 
831  | 
 
  | 
 
   | 
   | 
   | 
   | 
12  | 
 
  | 
   | 
799,000  | 
 
  | 
   | 
$  | 
125,829  | 
 
  | 
   | 
$  | 
5,636  | 
 
  | 
 
  
  
(1) This sale also included land 
 
In 2015, we completed dispositions of the following operating properties (dollars in thousands):
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Project Name  | 
   | 
City, State  | 
   | 
Segment  | 
   | 
Date of Disposition  | 
   | 
Number of Buildings  | 
   | 
Total Rentable Square Feet  | 
   | 
Transaction Value (1)  | 
   | 
Gain on Disposition  | 
 
1550 Westbranch Drive  | 
   | 
McLean, VA  | 
   | 
Regional Office  | 
   | 
7/27/2015  | 
   | 
1  | 
 
  | 
   | 
160,000  | 
 
  | 
   | 
$  | 
27,800  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
 
15000 and 15010 Conference Center Drive  | 
   | 
Chantilly, VA  | 
   | 
Northern Virginia Defense/IT  | 
   | 
8/28/2015  | 
   | 
2  | 
 
  | 
   | 
665,000  | 
 
  | 
   | 
167,335  | 
 
  | 
   | 
—  | 
 
  | 
 
13200 Woodland Park Road  | 
   | 
Herndon, VA  | 
   | 
Regional Office  | 
   | 
10/27/2015  | 
   | 
1  | 
 
  | 
   | 
397,000  | 
 
  | 
   | 
84,000  | 
 
  | 
   | 
42,515  | 
 
  | 
 
9900, 9910 and 9920 Franklin Square Drive  | 
   | 
White Marsh, MD  | 
   | 
Regional Office  | 
   | 
11/9/2015  | 
   | 
3  | 
 
  | 
   | 
135,000  | 
 
  | 
   | 
24,150  | 
 
  | 
   | 
6,468  | 
 
  | 
 
9690 Deereco Road and 375 W. Padonia Road  | 
   | 
Timonium, MD  | 
   | 
Regional Office  | 
   | 
12/17/2015  | 
   | 
2  | 
 
  | 
   | 
240,000  | 
 
  | 
   | 
44,500  | 
 
  | 
   | 
15,050  | 
 
  | 
 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
9  | 
 
  | 
   | 
1,597,000  | 
 
  | 
   | 
$  | 
347,785  | 
 
  | 
   | 
$  | 
64,033  | 
 
  | 
 
  
 
  
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(1)   | 
Each of these properties were sold except for 15000 and 15010 Conference Center Drive, the disposition of which was completed in connection with a debt extinguishment, as discussed further below.    | 
 
 
  
 
In 2016, we sold the following operating properties (dollars in thousands):
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Project Name  | 
   | 
City, State  | 
   | 
Segment  | 
   | 
Date of Sale  | 
   | 
Number of Buildings  | 
   | 
Total Rentable Square Feet  | 
   | 
Transaction Value  | 
   | 
Gain on Sale  | 
 
Arborcrest Corporate Campus (1)  | 
   | 
Philadelphia, PA  | 
   | 
Regional Office  | 
   | 
8/4/2016  | 
   | 
4  | 
 
  | 
   | 
654,000  | 
 
  | 
   | 
$  | 
142,800  | 
 
  | 
   | 
$  | 
4,742  | 
 
  | 
 
8003 Corporate Drive  | 
   | 
White Marsh, MD  | 
   | 
Regional Office  | 
   | 
8/17/2016  | 
   | 
1  | 
 
  | 
   | 
18,000  | 
 
  | 
   | 
2,400  | 
 
  | 
   | 
—  | 
 
  | 
 
1341 & 1343 Ashton Road  | 
   | 
Hanover, MD  | 
   | 
Fort Meade/BW Corridor  | 
   | 
9/9/2016  | 
   | 
2  | 
 
  | 
   | 
25,000  | 
 
  | 
   | 
2,900  | 
 
  | 
   | 
848  | 
 
  | 
 
8007, 8013, 8015, 8019 and 8023-8027 Corporate Drive (1)  | 
   | 
White Marsh, MD  | 
   | 
Regional Office  | 
   | 
9/21/2016  | 
   | 
5  | 
 
  | 
   | 
130,000  | 
 
  | 
   | 
14,513  | 
 
  | 
   | 
1,906  | 
 
  | 
 
1302, 1304 and 1306 Concourse Drive  | 
   | 
Linthicum, MD  | 
   | 
Fort Meade/BW Corridor  | 
   | 
9/29/2016  | 
   | 
3  | 
 
  | 
   | 
299,000  | 
 
  | 
   | 
48,100  | 
 
  | 
   | 
8,375  | 
 
  | 
 
2900 Towerview Road  | 
   | 
Herndon, VA  | 
   | 
Northern Virginia Defense/IT  | 
   | 
10/19/2016  | 
   | 
1  | 
 
  | 
   | 
151,000  | 
 
  | 
   | 
12,100  | 
 
  | 
   | 
—  | 
 
  | 
 
4940 Campbell Boulevard  | 
   | 
White Marsh, MD  | 
   | 
Regional Office  | 
   | 
11/17/2016  | 
   | 
1  | 
 
  | 
   | 
50,000  | 
 
  | 
   | 
5,200  | 
 
  | 
   | 
—  | 
 
  | 
 
1560 A and B Cable Ranch Road  | 
   | 
San Antonio, TX  | 
   | 
Other  | 
   | 
11/30/2016  | 
   | 
2  | 
 
  | 
   | 
120,000  | 
 
  | 
   | 
10,300  | 
 
  | 
   | 
—  | 
 
  | 
 
1331 Ashton Road  | 
   | 
Hanover, MD  | 
   | 
Fort Meade/BW Corridor  | 
   | 
12/19/2016  | 
   | 
1  | 
 
  | 
   | 
29,000  | 
 
  | 
   | 
2,625  | 
 
  | 
   | 
—  | 
 
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900 Elkridge Landing Road  | 
   | 
Linthicum, MD  | 
   | 
Fort Meade/BW Corridor  | 
   | 
12/22/2016  | 
   | 
1  | 
 
  | 
   | 
101,000  | 
 
  | 
   | 
7,800  | 
 
  | 
   | 
—  | 
 
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   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
21  | 
 
  | 
   | 
1,577,000  | 
 
  | 
   | 
$  | 
248,738  | 
 
  | 
   | 
$  | 
15,871  | 
 
  | 
 
  
 
  
(1) This sale also included land. 
  
 
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