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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 |  |  |  |

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- Definition Amount of facility held for productive use including, but not limited to, office, production, storage and distribution facilities, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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