Annual report pursuant to Section 13 and 15(d)

Properties, Net (Details 5)

v3.8.0.1
Properties, Net (Details 5)
$ / shares in Units, $ in Thousands
 12 Months Ended
Aug. 07, 2015
USD ($)
ft²
Apr. 15, 2015
USD ($)
ft²
Mar. 19, 2015
USD ($)
ft²
Dec. 31, 2017
USD ($)
ft²
Property
Dec. 31, 2016
USD ($)
ft²
Property
Dec. 31, 2015
USD ($)
ft²
Property
$ / shares
Business Combination            
Weighted average amortization period of intangible assets       11 years    
Pro Forma Information            
Pro forma total revenues           $ 641,982
Pro forma net income attributable to COPT common shareholders           $ 167,079
Basic (in dollars per share) | $ / shares           $ 1.77
Diluted (in dollars per share) | $ / shares           $ 1.77
Tenant relationship value [Member]            
Business Combination            
Weighted average amortization period of intangible assets       8 years    
Below-market cost arrangements [Member]            
Business Combination            
Weighted average amortization period of intangible assets       34 years    
2015 Property Acquisitions [Member]            
Business Combination            
Land, operating properties           $ 55,076
Building and improvements           139,540
Intangible assets on real estate acquisitions           75,729
Total assets           270,345
Below-market leases           (6,808)
Total acquisition cost           263,537
Finite-lived intangible assets acquired           $ 75,729
Weighted average amortization period of intangible assets           10 years
Contributed revenues       $ 38,100 $ 36,900 $ 20,200
Net income from continuing operations since acquisition date       $ 1,900 2,200 1,200
Acquisition related costs         $ 4,100  
2015 Property Acquisitions [Member] | Tenant relationship value [Member]            
Business Combination            
Finite-lived intangible assets acquired           $ 31,183
Weighted average amortization period of intangible assets           12 years
2015 Property Acquisitions [Member] | In-place lease value [Member]            
Business Combination            
Finite-lived intangible assets acquired           $ 35,139
Weighted average amortization period of intangible assets           7 years
2015 Property Acquisitions [Member] | Above-market leases [Member]            
Business Combination            
Finite-lived intangible assets acquired           $ 6,720
Weighted average amortization period of intangible assets           4 years
2015 Property Acquisitions [Member] | Below-market cost arrangements [Member]            
Business Combination            
Finite-lived intangible assets acquired           $ 2,687
Weighted average amortization period of intangible assets           40 years
Newly-constructed properties placed in service [Member]            
Business Acquisition [Line Items]            
Number of real estate properties | Property       8 6 7
Square footage of real estate properties (in square feet) | ft²       1,100,000 639,000 897,000
Newly redeveloped properties placed In service [Member]            
Business Acquisition [Line Items]            
Number of real estate properties | Property       3 3 2
Square footage of real estate properties (in square feet) | ft²       94,000 61,000 170,000
Properties under construction or contractually committed for construction [Member]            
Business Acquisition [Line Items]            
Number of real estate properties | Property       9    
Square footage of real estate properties (in square feet) | ft²       1,100,000    
Properties under redevelopment [Member]            
Business Acquisition [Line Items]            
Number of real estate properties | Property       1    
Square footage of real estate properties (in square feet) | ft²       22,000    
Office properties under, or contractually committed for, construction or approved for redevelopment [Member]            
Business Acquisition [Line Items]            
Number of real estate properties | Property       10    
Square footage of real estate properties (in square feet) | ft²       1,100,000    
Office properties under, or contractually committed for, construction or approved for redevelopment [Member] | Properties completed Held-for-future lease [Member]            
Business Acquisition [Line Items]            
Number of real estate properties | Property       2    
Regional Office [Member] | 250 W Pratt St [Member] | Baltimore, Maryland [Member]            
Business Acquisition [Line Items]            
Square footage of real estate properties (in square feet) | ft²     367,000      
Acquired property percentage leased     96.20%      
Purchase price     $ 61,800      
Regional Office [Member] | 100 and 30 Light Street [Member] | Baltimore, Maryland [Member]            
Business Acquisition [Line Items]            
Square footage of real estate properties (in square feet) | ft² 558,000          
Acquired property percentage leased 93.50%          
Purchase price $ 121,200          
Liabilities incurred 55,000          
Fair value assumption of debt $ 55,500          
Northern Virginia [Member] | Defense/Information Technology Sector [Member] | 2600 Park Tower Drive [Member] | Vienna, Virginia [Member]            
Business Acquisition [Line Items]            
Square footage of real estate properties (in square feet) | ft²   237,000        
Acquired property percentage leased   100.00%        
Purchase price   $ 80,500