Real Estate Partnerships (Summarized Operating Results and Financial Position of Partnership) (Details) - USD ($) $ in Thousands		3 Months Ended											12 Months Ended
	Jul. 24, 2014	Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014		Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
OPERATING RESULTS
Revenue		$ 192,507		$ 185,252	$ 181,461		$ 184,792	$ 176,377	$ 170,938		$ 167,947	$ 170,828	$ 744,012	$ 686,090	$ 637,413
Depreciation and amortization													174,796	170,814	160,828
Interest expense													92,553	93,941	104,977
Income before gain on sale of real estate													190,094	167,888	162,614
Gain on sale of real estate													28,330	4,401	4,994
Net income		69,998	[1]	$ 54,550	$ 45,673	[1]	$ 48,203	37,279	49,049	[1]	$ 45,416	$ 40,545	218,424	172,289	167,608
ASSETS
Real estate, net		4,490,365						4,141,948					4,490,365	4,141,948
Cash		21,046						47,951					21,046	47,951	88,927	$ 36,988
Total assets		4,911,709						4,546,870					4,911,709	4,546,870
LIABILITIES AND PARTNERS' CAPITAL
Mortgages payable		482,822						563,698					482,822	563,698
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY		4,911,709						4,546,870					4,911,709	4,546,870
Our investment in real estate partnership		41,546						37,457					41,546	37,457
Federal Realty Investment Trust/Clarion Partners Partnership
OPERATING RESULTS
Revenue													17,405	18,329	19,209
Other operating expenses													5,992	5,948	5,999
Depreciation and amortization													4,974	5,678	5,506
Interest expense													2,062	2,759	3,363
Total expenses													13,028	14,385	14,868
Income before gain on sale of real estate													4,377	3,944	4,341
Gain on sale of real estate	$ 14,500												0	14,507	0
Net income													4,377	18,451	4,341
ASSETS
Real estate, net		146,906						149,203					146,906	149,203
Cash		2,690						2,864					2,690	2,864
Other assets		5,495						5,346					5,495	5,346
Total assets		155,091						157,413					155,091	157,413
LIABILITIES AND PARTNERS' CAPITAL
Mortgages payable		34,385						34,385					34,385	34,385
Other liabilities		3,554						3,673					3,554	3,673
Partners’ capital		117,152						119,355					117,152	119,355
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY		155,091						157,413					155,091	157,413
Our share of unconsolidated debt		10,316						10,316					10,316	10,316
Our investment in real estate partnership		$ 31,745						$ 32,367					31,745	32,367
Federal Realty Investment Trust | Federal Realty Investment Trust/Clarion Partners Partnership
OPERATING RESULTS
Gain on sale of real estate	$ 4,400								$ 4,400
Our share of net income from real estate partnership before gain on sale of real estate													1,557	1,423	1,498
Our share of gain on sale of real estate													$ 0	$ 4,401	$ 0

[1] (1)Second and fourth quarter 2015 include an $11.5 million and $16.8 million gain on sale, respectively, from our Houston Street and Courtyard Shops properties as further discussed in Note 3. Third quarter 2014 includes a $4.4 million gain on sale reflecting our share of the Partnership's sale of Pleasant Shops as further discussed in Note 5.