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Real Estate Transactions (Narrative) (Details) (USD $)
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12 Months Ended | 12 Months Ended | 0 Months Ended | 3 Months Ended | 0 Months Ended | 3 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | |||||||||||||||||||||||||||||
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2012
Roseland Partners LLC [Member]
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Jan. 25, 2013
Roseland Partners LLC [Member]
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Oct. 23, 2012
Roseland Partners LLC [Member]
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Dec. 31, 2012
Roseland Partners LLC [Member]
Multi-Family Properties [Member]
item
property
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Dec. 31, 2012
Roseland Partners LLC [Member]
Condo-Residential Properties [Member]
property
item
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Dec. 31, 2012
Roseland Partners LLC [Member]
Commercial Properties [Member]
sqft
property
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Dec. 31, 2012
Roseland Partners LLC [Member]
In-Process Development Projects [Member]
property
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Dec. 31, 2012
Roseland Partners LLC [Member]
In-Process Development Projects [Member]
Multi-Family Properties [Member]
item
property
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Dec. 31, 2012
Roseland Partners LLC [Member]
In-Process Development Projects [Member]
Garages [Member]
property
item
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Dec. 31, 2012
Roseland Partners LLC [Member]
In-Process Development Projects [Member]
Retail [Member]
property
sqft
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Dec. 31, 2012
Roseland Partners LLC [Member]
Interests Or Options In Land Parcels [Member]
Multi-Family Properties [Member]
item
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Dec. 31, 2012
Roseland Partners LLC [Member]
Interests Or Options In Land Parcels [Member]
Commercial Properties [Member]
sqft
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Dec. 31, 2012
Roseland Partners LLC [Member]
Interests Or Options In Land Parcels [Member]
Hotel [Member]
item
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Jan. 18, 2013
Alterra At Overlook Ridge IA [Member]
item
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Jan. 17, 2013
Alterra At Overlook Ridge IB [Member]
item
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Jul. 25, 2012
95 Chestnut Ridge Road [Member]
sqft
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Mar. 31, 2012
95 Chestnut Ridge Road [Member]
sqft
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Nov. 07, 2013
Strawbridge Drive [Member]
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Nov. 07, 2012
Strawbridge Drive [Member]
property
sqft
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Jun. 30, 2012
Strawbridge Drive [Member]
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Dec. 31, 2012
19 Skyline Drive [Member]
sqft
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Dec. 31, 2012
55 Corporate Drive [Member]
sqft
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Dec. 31, 2012
19 Skyline Drive And 55 Corporate Drive [Member]
property
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Dec. 31, 2012
East Rutherford, New Jersey Property [Member]
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Dec. 31, 2012
Newark, New Jersey [Member]
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Dec. 31, 2012
9200 Edmonston Road [Member]
sqft
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Dec. 31, 2012
16 And 18 Sentry Parkway [Member]
property
sqft
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Jan. 17, 2013
Scenario, Forecast [Member]
Alterra At Overlook Ridge IB [Member]
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Dec. 31, 2012
Roseland Assets [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Completion Of Certain Developments [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Start Of Construction On Certain Developments [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Obtaining Of Tax Credits/Grants [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Total Return To Shareholders [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Failure To Achieve A Certain Level Of Fee Revenue [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Minimum [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Minimum [Member]
Completion And Start Of Certain Developments [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Maximum [Member]
Roseland Partners LLC [Member]
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Dec. 31, 2012
Maximum [Member]
Completion And Start Of Certain Developments [Member]
Roseland Partners LLC [Member]
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| Real Estate Transactions [Line Items] | ||||||||||||||||||||||||||||||||||||||||
| Number of real estate properties | 6 | 1 | 4 | 13 | 9 | 2 | 2 | 3 | 2 | |||||||||||||||||||||||||||||||
| Number of units | 1,769 | 3 | 2,149 | 5,980 | 321 | 310 | 412 | |||||||||||||||||||||||||||||||||
| Area of property (in square feet) | 212,000 | 35,400 | 736,000 | 47,700 | 47,700 | 222,258 | 248,400 | 204,057 | 38,690 | 188,103 | ||||||||||||||||||||||||||||||
| Number of parking spaces | 1,591 | |||||||||||||||||||||||||||||||||||||||
| Aggregate consideration for acquisition | $ 115,602,000 | |||||||||||||||||||||||||||||||||||||||
| Business acquisition, cash paid | 115,579,000 | 61,300,000 | 88,000,000 | |||||||||||||||||||||||||||||||||||||
| Fair value of contingent consideration | 10,010,000 | 6,300,000 | 3,700,000 | |||||||||||||||||||||||||||||||||||||
| Business acquisition, debt assumed | 22,000,000 | |||||||||||||||||||||||||||||||||||||||
| Business acquisition, contingent cash payment | 15,600,000 | 8,600,000 | 2,800,000 | 2,800,000 | 3,000,000 | 7,000,000 | 2,000,000 | |||||||||||||||||||||||||||||||||
| Business acquisition, earn out period | 3 years | 3 years | ||||||||||||||||||||||||||||||||||||||
| Probability of occurrence of contingent consideration payment events | 50.00% | 92.00% | 99.00% | |||||||||||||||||||||||||||||||||||||
| Goodwill | 2,945,000 | 2,945,000 | ||||||||||||||||||||||||||||||||||||||
| Contingent purchase price measurement period | 33 months | |||||||||||||||||||||||||||||||||||||||
| Amount of cash deposited to escrow | 34,000,000 | |||||||||||||||||||||||||||||||||||||||
| Discount rate | 10.00% | 15.00% | ||||||||||||||||||||||||||||||||||||||
| Direct cap rate | 5.00% | 7.50% | ||||||||||||||||||||||||||||||||||||||
| Earn out paid | 2,800,000 | |||||||||||||||||||||||||||||||||||||||
| Transaction costs | 5,800,000 | |||||||||||||||||||||||||||||||||||||||
| Proceeds from the sale of property | 23,429,000 | 4,000,000 | 19,400,000 | |||||||||||||||||||||||||||||||||||||
| Valuation allowance recognized | 500,000 | 1,600,000 | 7,100,000 | 7,100,000 | ||||||||||||||||||||||||||||||||||||
| Loss on sale of property | 100,000 | |||||||||||||||||||||||||||||||||||||||
| Number of properties held for sale | 2 | |||||||||||||||||||||||||||||||||||||||
| Value of property held for sale | 60,900,000 | |||||||||||||||||||||||||||||||||||||||
| Accumulated depreciation | 1,478,214,000 | 1,409,163,000 | 16,800,000 | |||||||||||||||||||||||||||||||||||||
| Impairment charge | 6,300,000 | 500,000 | 3,000,000 | 8,400,000 | ||||||||||||||||||||||||||||||||||||
| Investment in property | 3,901,222,000 | 3,870,607,000 | 11,900,000 | |||||||||||||||||||||||||||||||||||||
| Estimated amount recoverable at sale | 5,600,000 | |||||||||||||||||||||||||||||||||||||||
| Mortgage loan, maturity date | May 1, 2013 | |||||||||||||||||||||||||||||||||||||||
| Mortgage loans, carrying amount | $ 4,300,000 | |||||||||||||||||||||||||||||||||||||||