Real Estate Partnerships (Summarized Operating Results and Financial Position of Partnership) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended													12 Months Ended			0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014		Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 24, 2014	Dec. 31, 2011
OPERATING RESULTS
Revenue	$ 176,377	$ 170,938		$ 167,947	$ 170,828	$ 163,846	[1]	$ 159,030	[1]	$ 157,388	[1]	$ 157,149	[1]	$ 686,090	$ 637,413	$ 605,791
Depreciation and amortization														170,814	160,828	141,701
Interest expense														93,941	104,977	113,336
Income before gain on sale of real estate														167,888	162,614	144,372
Gain on sale of real estate														4,401	4,994	11,860
Net income	37,279	49,049	[2]	45,416	40,545	29,603		63,366	[2]	38,797		35,842		172,289	167,608	156,232
Our share of net income from real estate partnership before gain on sale of real estate														1,243	1,498	1,757
ASSETS
Real estate, net	4,141,948					3,798,992								4,141,948	3,798,992
Cash	47,951					88,927								47,951	88,927	36,988		67,806
Total assets	4,546,870					4,219,294								4,546,870	4,219,294
LIABILITIES AND PARTNERS' CAPITAL
Mortgages payable	563,698					588,456								563,698	588,456
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	4,546,870					4,219,294								4,546,870	4,219,294
Our investment in real estate partnership	37,457					32,264								37,457	32,264
Federal / Lion Venture LP
OPERATING RESULTS
Revenue														18,329	19,209	19,051
Other operating expenses														5,948	5,999	5,234
Depreciation and amortization														5,678	5,506	5,508
Interest expense														2,759	3,363	3,376
Total expenses														14,385	14,868	14,118
Income before gain on sale of real estate														3,944	4,341	4,933
Gain on sale of real estate														14,507	0	0	14,500
Net income														18,451	4,341	4,933
ASSETS
Real estate, net	149,203					170,867								149,203	170,867
Cash	2,864					2,210								2,864	2,210
Other assets	5,346					5,668								5,346	5,668
Total assets	157,413					178,745								157,413	178,745
LIABILITIES AND PARTNERS' CAPITAL
Mortgages payable	34,385					56,922								34,385	56,922
Other liabilities	3,673					4,100								3,673	4,100
Partners’ capital	119,355					117,723								119,355	117,723
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	157,413					178,745								157,413	178,745
Our share of unconsolidated debt	10,316					17,077								10,316	17,077
Our investment in real estate partnership	32,367					32,264								32,367	32,264
Federal Realty Investment Trust | Federal / Lion Venture LP
OPERATING RESULTS
Gain on sale of real estate																	4,400
Our share of net income from real estate partnership before gain on sale of real estate														1,423	1,498	1,815
Our share of gain on sale of real estate														$ 4,401	$ 0	$ 0

[1] Revenue in 2013 has been reduced to reflect the results of discontinued operations as further discussed in Note 14. Revenue from discontinued operations, by quarter, is summarized as follows: FirstQuarter SecondQuarter ThirdQuarter FourthQuarter (In thousands)2013 revenue from discontinued operations$602 $559 $385 $—

[2] 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. Third quarter 2013 includes a $23.9 million gain on sale of two retail buildings as further discussed in Note 3.