| 
           Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Tables)
  
         | 
        6 Months Ended | 
      
      
        | 
           Jun. 30, 2014 
         | 
      
      
        | 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): 
 |  
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
   | 
For the Three Months Ended June 30,  | 
   | 
For the Six Months Ended June 30,  | 
 
   | 
2014  | 
   | 
2013  | 
   | 
2014  | 
   | 
2013  | 
 
Numerator:  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Income (loss) from continuing operations  | 
$  | 
9,248  | 
 
  | 
   | 
$  | 
(232  | 
)  | 
   | 
$  | 
14,908  | 
 
  | 
   | 
$  | 
11,430  | 
 
  | 
 
Gain on sales of real estate, net  | 
—  | 
 
  | 
   | 
329  | 
 
  | 
   | 
—  | 
 
  | 
   | 
2,683  | 
 
  | 
 
Preferred share dividends  | 
(4,344  | 
)  | 
   | 
(4,885  | 
)  | 
   | 
(8,834  | 
)  | 
   | 
(10,991  | 
)  | 
 
Issuance costs associated with redeemed preferred shares  | 
(1,769  | 
)  | 
   | 
(2,904  | 
)  | 
   | 
(1,769  | 
)  | 
   | 
(2,904  | 
)  | 
 
Income from continuing operations attributable to noncontrolling interests  | 
(1,171  | 
)  | 
   | 
(1,087  | 
)  | 
   | 
(2,103  | 
)  | 
   | 
(1,254  | 
)  | 
 
Income from continuing operations attributable to restricted shares  | 
(108  | 
)  | 
   | 
(102  | 
)  | 
   | 
(229  | 
)  | 
   | 
(220  | 
)  | 
 
Numerator for basic EPS from continuing operations attributable to COPT common shareholders  | 
1,856  | 
 
  | 
   | 
(8,881  | 
)  | 
   | 
1,973  | 
 
  | 
   | 
(1,256  | 
)  | 
 
Dilutive effect of common units in COPLP on diluted EPS from continuing operations  | 
—  | 
 
  | 
   | 
(478  | 
)  | 
   | 
—  | 
 
  | 
   | 
(108  | 
)  | 
 
Numerator for diluted EPS from continuing operations attributable to COPT common shareholders  | 
$  | 
1,856  | 
 
  | 
   | 
$  | 
(9,359  | 
)  | 
   | 
$  | 
1,973  | 
 
  | 
   | 
$  | 
(1,364  | 
)  | 
 
Numerator for basic EPS from continuing operations attributable to COPT common shareholders  | 
$  | 
1,856  | 
 
  | 
   | 
$  | 
(8,881  | 
)  | 
   | 
$  | 
1,973  | 
 
  | 
   | 
$  | 
(1,256  | 
)  | 
 
Discontinued operations  | 
(198  | 
)  | 
   | 
(4,502  | 
)  | 
   | 
(187  | 
)  | 
   | 
(3,241  | 
)  | 
 
Discontinued operations attributable to noncontrolling interests  | 
11  | 
 
  | 
   | 
127  | 
 
  | 
   | 
13  | 
 
  | 
   | 
37  | 
 
  | 
 
Numerator for basic EPS on net income (loss) attributable to COPT common shareholders  | 
1,669  | 
 
  | 
   | 
(13,256  | 
)  | 
   | 
1,799  | 
 
  | 
   | 
(4,460  | 
)  | 
 
Dilutive effect of common units in COPLP  | 
—  | 
 
  | 
   | 
(671  | 
)  | 
   | 
—  | 
 
  | 
   | 
(242  | 
)  | 
 
Numerator for diluted EPS on net income (loss) attributable to COPT common shareholders  | 
$  | 
1,669  | 
 
  | 
   | 
$  | 
(13,927  | 
)  | 
   | 
$  | 
1,799  | 
 
  | 
   | 
$  | 
(4,702  | 
)  | 
 
Denominator (all weighted averages):  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Denominator for basic EPS (common shares)  | 
87,214  | 
 
  | 
   | 
85,425  | 
 
  | 
   | 
87,148  | 
 
  | 
   | 
83,422  | 
 
  | 
 
Dilutive effect of common units  | 
—  | 
 
  | 
   | 
3,801  | 
 
  | 
   | 
—  | 
 
  | 
   | 
3,847  | 
 
  | 
 
Dilutive effect of share-based compensation awards  | 
201  | 
 
  | 
   | 
—  | 
 
  | 
   | 
156  | 
 
  | 
   | 
—  | 
 
  | 
 
Denominator for diluted EPS (common shares)   | 
87,415  | 
 
  | 
   | 
89,226  | 
 
  | 
   | 
87,304  | 
 
  | 
   | 
87,269  | 
 
  | 
 
Basic EPS:  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Income (loss) from continuing operations attributable to COPT common shareholders  | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.10  | 
)  | 
   | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.02  | 
)  | 
 
Discontinued operations attributable to COPT common shareholders  | 
0.00  | 
 
  | 
   | 
(0.06  | 
)  | 
   | 
0.00  | 
 
  | 
   | 
(0.03  | 
)  | 
 
Net income (loss) attributable to COPT common shareholders  | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.16  | 
)  | 
   | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.05  | 
)  | 
 
Diluted EPS:  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Income (loss) from continuing operations attributable to COPT common shareholders  | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.10  | 
)  | 
   | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.02  | 
)  | 
 
Discontinued operations attributable to COPT common shareholders  | 
0.00  | 
 
  | 
   | 
(0.06  | 
)  | 
   | 
0.00  | 
 
  | 
   | 
(0.03  | 
)  | 
 
Net income (loss) attributable to COPT common shareholders  | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.16  | 
)  | 
   | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.05  | 
)  | 
 
  
 
 | 
      
      
        | 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): 
 |  
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
   | 
Weighted Average Shares Excluded from Denominator  | 
 
   | 
For the Three Months Ended June 30,  | 
   | 
For the Six Months Ended June 30,  | 
 
   | 
2014  | 
   | 
2013  | 
   | 
2014  | 
   | 
2013  | 
 
Conversion of common units  | 
3,912  | 
 
  | 
   | 
—  | 
 
  | 
   | 
3,934  | 
 
  | 
   | 
—  | 
 
  | 
 
Conversion of Series I Preferred Units  | 
176  | 
 
  | 
   | 
176  | 
 
  | 
   | 
176  | 
 
  | 
   | 
176  | 
 
  | 
 
Conversion of Series K Preferred Shares  | 
434  | 
 
  | 
   | 
434  | 
 
  | 
   | 
434  | 
 
  | 
   | 
434  | 
 
  | 
 
  
 
 | 
      
      
        | 
           Corporate Office Properties, L.P. 
         | 
         
 | 
      
      
        | 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,  | 
 
   | 
2014  | 
   | 
2013  | 
   | 
2014  | 
   | 
2013  | 
 
Numerator:  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Income (loss) from continuing operations  | 
$  | 
9,248  | 
 
  | 
   | 
$  | 
(232  | 
)  | 
   | 
$  | 
14,908  | 
 
  | 
   | 
$  | 
11,430  | 
 
  | 
 
Gain on sales of real estate, net  | 
—  | 
 
  | 
   | 
329  | 
 
  | 
   | 
—  | 
 
  | 
   | 
2,683  | 
 
  | 
 
Preferred unit distributions  | 
(4,509  | 
)  | 
   | 
(5,050  | 
)  | 
   | 
(9,164  | 
)  | 
   | 
(11,321  | 
)  | 
 
Issuance costs associated with redeemed preferred units  | 
(1,769  | 
)  | 
   | 
(2,904  | 
)  | 
   | 
(1,769  | 
)  | 
   | 
(2,904  | 
)  | 
 
Income from continuing operations attributable to noncontrolling interests  | 
(840  | 
)  | 
   | 
(1,408  | 
)  | 
   | 
(1,579  | 
)  | 
   | 
(1,039  | 
)  | 
 
Income from continuing operations attributable to restricted units  | 
(108  | 
)  | 
   | 
(102  | 
)  | 
   | 
(229  | 
)  | 
   | 
(220  | 
)  | 
 
Numerator for basic and diluted EPU from continuing operations attributable to COPLP common unitholders  | 
$  | 
2,022  | 
 
  | 
   | 
$  | 
(9,367  | 
)  | 
   | 
$  | 
2,167  | 
 
  | 
   | 
$  | 
(1,371  | 
)  | 
 
Discontinued operations  | 
(198  | 
)  | 
   | 
(4,502  | 
)  | 
   | 
(187  | 
)  | 
   | 
(3,241  | 
)  | 
 
Discontinued operations attributable to noncontrolling interests  | 
3  | 
 
  | 
   | 
(65  | 
)  | 
   | 
5  | 
 
  | 
   | 
(98  | 
)  | 
 
Numerator for basic and diluted EPU on net income attributable to COPLP common unitholders  | 
$  | 
1,827  | 
 
  | 
   | 
$  | 
(13,934  | 
)  | 
   | 
$  | 
1,985  | 
 
  | 
   | 
$  | 
(4,710  | 
)  | 
 
Denominator (all weighted averages):  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Denominator for basic EPU (common units)  | 
91,126  | 
 
  | 
   | 
89,226  | 
 
  | 
   | 
91,082  | 
 
  | 
   | 
87,269  | 
 
  | 
 
Dilutive effect of share-based compensation awards  | 
201  | 
 
  | 
   | 
—  | 
 
  | 
   | 
156  | 
 
  | 
   | 
—  | 
 
  | 
 
Denominator for basic and diluted EPU (common units)  | 
91,327  | 
 
  | 
   | 
89,226  | 
 
  | 
   | 
91,238  | 
 
  | 
   | 
87,269  | 
 
  | 
 
Basic EPU:  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Income (loss) from continuing operations attributable to COPLP common unitholders  | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.10  | 
)  | 
   | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.02  | 
)  | 
 
Discontinued operations attributable to COPLP common unitholders  | 
0.00  | 
 
  | 
   | 
(0.06  | 
)  | 
   | 
0.00  | 
 
  | 
   | 
(0.03  | 
)  | 
 
Net income (loss) attributable to COPLP common unitholders  | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.16  | 
)  | 
   | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.05  | 
)  | 
 
Diluted EPU:  | 
   | 
 
  | 
   | 
   | 
 
  | 
   | 
   | 
   | 
   | 
 
Income (loss) from continuing operations attributable to COPLP common unitholders  | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.10  | 
)  | 
   | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.02  | 
)  | 
 
Discontinued operations attributable to COPLP common unitholders  | 
0.00  | 
 
  | 
   | 
(0.06  | 
)  | 
   | 
0.00  | 
 
  | 
   | 
(0.03  | 
)  | 
 
Net income (loss) attributable to COPLP common unitholders  | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.16  | 
)  | 
   | 
$  | 
0.02  | 
 
  | 
   | 
$  | 
(0.05  | 
)  | 
 
  
 
 | 
      
      
        | 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 Units Excluded from Denominator  | 
 
   | 
For the Three Months Ended June 30,  | 
   | 
For the Six Months Ended June 30,  | 
 
   | 
2014  | 
   | 
2013  | 
   | 
2014  | 
   | 
2013  | 
 
Conversion of Series I preferred units  | 
176  | 
 
  | 
   | 
176  | 
 
  | 
   | 
176  | 
 
  | 
   | 
176  | 
 
  | 
 
Conversion of Series K preferred units  | 
434  | 
 
  | 
   | 
434  | 
 
  | 
   | 
434  | 
 
  | 
   | 
434  | 
 
  | 
 
  
 
 |