Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Tables)
   | 
6 Months Ended | 
Jun. 30, 2019  | 
| Earnings Per Share [Line Items] | 
 
 | 
| Summary of calculation of numerator and denominator in basic and diluted earnings per share | 
 Summaries of the numerator and denominator for purposes of basic and diluted EPS calculations are set forth below (in thousands, except per share data): 
 |  
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   | 
For the Three Months Ended June 30,   | 
   | 
For the Six Months Ended June 30,  | 
 
   | 
2019  | 
   | 
2018  | 
   | 
2019  | 
   | 
2018  | 
 
Numerator:  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Net income attributable to COPT  | 
$  | 
106,791  | 
 
  | 
   | 
$  | 
19,434  | 
 
  | 
   | 
$  | 
127,650  | 
 
  | 
   | 
$  | 
36,584  | 
 
  | 
 
Income attributable to share-based compensation awards  | 
(364  | 
)  | 
   | 
(117  | 
)  | 
   | 
(413  | 
)  | 
   | 
(234  | 
)  | 
 
Numerator for basic EPS on net income attributable to COPT common shareholders  | 
106,427  | 
 
  | 
   | 
19,317  | 
 
  | 
   | 
127,237  | 
 
  | 
   | 
36,350  | 
 
  | 
 
Preferred unit distributions  | 
165  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
 
Redeemable noncontrolling interests  | 
902  | 
 
  | 
   | 
—  | 
 
  | 
   | 
66  | 
 
  | 
   | 
—  | 
 
  | 
 
Common units in the Operating Partnership  | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
1,515  | 
 
  | 
   | 
—  | 
 
  | 
 
Income attributable to share-based compensation awards  | 
18  | 
 
  | 
   | 
—  | 
 
  | 
   | 
22  | 
 
  | 
   | 
—  | 
 
  | 
 
Numerator for diluted EPS on net income attributable to COPT common shareholders  | 
$  | 
107,512  | 
 
  | 
   | 
$  | 
19,317  | 
 
  | 
   | 
$  | 
128,840  | 
 
  | 
   | 
$  | 
36,350  | 
 
  | 
 
Denominator (all weighted averages):  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Denominator for basic EPS (common shares)  | 
111,557  | 
 
  | 
   | 
101,789  | 
 
  | 
   | 
110,759  | 
 
  | 
   | 
101,397  | 
 
  | 
 
Dilutive convertible preferred units  | 
176  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
 
Dilutive effect of common units  | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
1,329  | 
 
  | 
   | 
—  | 
 
  | 
 
Dilutive effect of share-based compensation awards  | 
310  | 
 
  | 
   | 
119  | 
 
  | 
   | 
289  | 
 
  | 
   | 
131  | 
 
  | 
 
Dilutive effect of redeemable noncontrolling interests  | 
1,062  | 
 
  | 
   | 
—  | 
 
  | 
   | 
130  | 
 
  | 
   | 
—  | 
 
  | 
 
Denominator for diluted EPS (common shares)   | 
113,105  | 
 
  | 
   | 
101,908  | 
 
  | 
   | 
112,507  | 
 
  | 
   | 
101,528  | 
 
  | 
 
Basic EPS  | 
$  | 
0.95  | 
 
  | 
   | 
$  | 
0.19  | 
 
  | 
   | 
$  | 
1.15  | 
 
  | 
   | 
$  | 
0.36  | 
 
  | 
 
Diluted EPS  | 
$  | 
0.95  | 
 
  | 
   | 
$  | 
0.19  | 
 
  | 
   | 
$  | 
1.15  | 
 
  | 
   | 
$  | 
0.36  | 
 
  | 
 
  
 
 
 | 
| Schedule of securities excluded from computation of diluted earnings per share | 
 Our diluted EPS computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPS for the respective periods (in thousands): 
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 | 
 | 
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 | 
 | 
 | 
 | 
 
   | 
Weighted Average Shares Excluded from Denominator  | 
 
   | 
For the Three Months Ended June 30,   | 
   | 
For the Six Months Ended June 30,  | 
 
   | 
2019  | 
   | 
2018  | 
   | 
2019  | 
   | 
2018  | 
 
Conversion of common units  | 
1,327  | 
 
  | 
   | 
3,197  | 
 
  | 
   | 
—  | 
 
  | 
   | 
3,208  | 
 
  | 
 
Conversion of redeemable noncontrolling interests  | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
907  | 
 
  | 
   | 
—  | 
 
  | 
 
Conversion of Series I preferred units  | 
—  | 
 
  | 
   | 
176  | 
 
  | 
   | 
176  | 
 
  | 
   | 
176  | 
 
  | 
 
  
 
 
 | 
| Corporate Office Properties, L.P. | 
 
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| Earnings Per Share [Line Items] | 
 
 | 
| Summary of calculation of numerator and denominator in basic and diluted earnings per share | 
 Summaries of the numerator and denominator for purposes of basic and diluted EPU calculations are set forth below (in thousands, except per unit data): 
 |  
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
   | 
For the Three Months Ended June 30,   | 
   | 
For the Six Months Ended June 30,  | 
 
   | 
2019  | 
   | 
2018  | 
   | 
2019  | 
   | 
2018  | 
 
Numerator:  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Net income attributable to COPLP  | 
$  | 
108,295  | 
 
  | 
   | 
$  | 
20,207  | 
 
  | 
   | 
$  | 
129,576  | 
 
  | 
   | 
$  | 
38,066  | 
 
  | 
 
Preferred unit distributions  | 
(165  | 
)  | 
   | 
(165  | 
)  | 
   | 
(330  | 
)  | 
   | 
(330  | 
)  | 
 
Income attributable to share-based compensation awards  | 
(438  | 
)  | 
   | 
(117  | 
)  | 
   | 
(494  | 
)  | 
   | 
(234  | 
)  | 
 
Numerator for basic EPU on net income attributable to COPLP common unitholders  | 
107,692  | 
 
  | 
   | 
19,925  | 
 
  | 
   | 
128,752  | 
 
  | 
   | 
37,502  | 
 
  | 
 
Redeemable noncontrolling interests  | 
902  | 
 
  | 
   | 
—  | 
 
  | 
   | 
66  | 
 
  | 
   | 
—  | 
 
  | 
 
Income attributable to share-based compensation awards  | 
18  | 
 
  | 
   | 
—  | 
 
  | 
   | 
22  | 
 
  | 
   | 
—  | 
 
  | 
 
Dilutive effective of preferred units  | 
165  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
 
Numerator for diluted EPU on net income attributable to COPLP common unitholders  | 
$  | 
108,777  | 
 
  | 
   | 
$  | 
19,925  | 
 
  | 
   | 
$  | 
128,840  | 
 
  | 
   | 
$  | 
37,502  | 
 
  | 
 
Denominator (all weighted averages):  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Denominator for basic EPU (common units)  | 
112,884  | 
 
  | 
   | 
104,986  | 
 
  | 
   | 
112,088  | 
 
  | 
   | 
104,605  | 
 
  | 
 
Dilutive convertible preferred units  | 
176  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
 
Dilutive effect of redeemable noncontrolling interests  | 
1,062  | 
 
  | 
   | 
—  | 
 
  | 
   | 
130  | 
 
  | 
   | 
—  | 
 
  | 
 
Dilutive effect of share-based compensation awards  | 
310  | 
 
  | 
   | 
119  | 
 
  | 
   | 
289  | 
 
  | 
   | 
131  | 
 
  | 
 
Denominator for diluted EPU (common units)  | 
114,432  | 
 
  | 
   | 
105,105  | 
 
  | 
   | 
112,507  | 
 
  | 
   | 
104,736  | 
 
  | 
 
Basic EPU  | 
$  | 
0.95  | 
 
  | 
   | 
$  | 
0.19  | 
 
  | 
   | 
$  | 
1.15  | 
 
  | 
   | 
$  | 
0.36  | 
 
  | 
 
Diluted EPU  | 
$  | 
0.95  | 
 
  | 
   | 
$  | 
0.19  | 
 
  | 
   | 
$  | 
1.15  | 
 
  | 
   | 
$  | 
0.36  | 
 
  | 
 
  
 
 
 | 
| Schedule of securities excluded from computation of diluted earnings per share | 
Our diluted EPU computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPU for the respective periods (in thousands): 
 |  
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
   | 
Weighted Average Shares Excluded from Denominator  | 
 
   | 
For the Three Months Ended June 30,   | 
   | 
For the Six Months Ended June 30,  | 
 
   | 
2019  | 
   | 
2018  | 
   | 
2019  | 
   | 
2018  | 
 
Conversion of redeemable noncontrolling interests  | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
907  | 
 
  | 
   | 
—  | 
 
  | 
 
Conversion of Series I preferred units  | 
—  | 
 
  | 
   | 
176  | 
 
  | 
   | 
176  | 
 
  | 
   | 
176  | 
 
  | 
 
  
 
 
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