Real Estate Partnerships - Summarized Operating Results and Financial Position of the Partnership (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
OPERATING RESULTS
Revenue	$ 181,461	$ 167,947	$ 366,253	$ 338,775
Expenses
Depreciation and amortization	42,671	40,893	84,655	84,743
Interest expense	23,445	23,213	47,613	46,350
Net income	45,673	45,416	93,876	85,961
Our share of net income from real estate partnership	406	250	626	463
BALANCE SHEETS
Real estate, net	4,335,782		4,335,782		$ 4,141,948
Cash	22,175	41,312	22,175	41,312	47,951	$ 88,927
TOTAL ASSETS	4,733,838		4,733,838		4,546,870
Mortgages payable	576,446		576,446		563,698
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	4,733,838		4,733,838		4,546,870
Our investment in real estate partnership	37,748		37,748		37,457
Federal Realty Investment Trust / ING Clarion Partners Partnership
OPERATING RESULTS
Revenue	4,273	4,469	9,017	9,487
Expenses
Other operating expenses	1,242	1,390	3,371	3,500
Depreciation and amortization	1,237	1,590	2,459	3,077
Interest expense	517	781	1,036	1,620
Total expenses	2,996	3,761	6,866	8,197
Net income	1,277	708	2,151	1,290
BALANCE SHEETS
Real estate, net	147,514		147,514		149,203
Cash	4,501		4,501		2,864
Other assets	5,709		5,709		5,346
TOTAL ASSETS	157,724		157,724		157,413
Mortgages payable	34,385		34,385		34,385
Other liabilities	3,201		3,201		3,673
Partners’ capital	120,138		120,138		119,355
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	157,724		157,724		157,413
Federal Realty Investment Trust | Federal Realty Investment Trust / ING Clarion Partners Partnership
Expenses
Our share of net income from real estate partnership	423	$ 250	722	$ 463
BALANCE SHEETS
Our share of unconsolidated debt	10,316		10,316		10,316
Our investment in real estate partnership	$ 32,535		$ 32,535		$ 32,367