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, 2016	Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING RESULTS
Revenue		$ 204,109	$ 201,157		$ 197,981		$ 198,344		$ 192,507		$ 185,252	$ 181,461		$ 184,792	$ 801,591	$ 744,012	$ 686,090
Depreciation and amortization															193,585	174,796	170,814
Interest expense															94,994	92,553	93,941
Net income		59,724	$ 61,198	[1]	$ 58,898	[1]	$ 79,063	[1]	69,998	[1]	$ 54,550	$ 45,673	[1]	$ 48,203	258,883	218,424	172,289
ASSETS
Real estate, net		5,029,839							4,490,365						5,029,839	4,490,365
Cash		23,368							21,046						23,368	21,046	47,951	$ 88,927
Total assets		5,423,279							4,896,559						5,423,279	4,896,559
LIABILITIES AND PARTNERS' CAPITAL
Mortgages payable		471,117							481,084						471,117	481,084
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY		5,423,279							4,896,559						5,423,279	4,896,559
Our investment in real estate partnership		$ 14,864							41,546						$ 14,864	41,546
Federal Realty Investment Trust/Clarion Partners Partnership
OPERATING RESULTS
Revenue																17,405	18,329
Other operating expenses																5,992	5,948
Depreciation and amortization																4,974	5,678
Interest expense																2,062	2,759
Total expenses																13,028	14,385
Income before gain on sale of real estate																4,377	3,944
Gain on sale of real estate	$ 14,500															0	14,507
Net income																4,377	18,451
ASSETS
Real estate, net									146,906							146,906
Cash									2,690							2,690
Other assets									5,495							5,495
Total assets									155,091							155,091
LIABILITIES AND PARTNERS' CAPITAL
Mortgages payable									34,385							34,385
Other liabilities									3,554							3,554
Partners’ capital									117,152							117,152
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY									155,091							155,091
Our share of unconsolidated debt									10,316							10,316
Our investment in real estate partnership									$ 31,745							31,745
Federal Realty Investment Trust | Federal Realty Investment Trust/Clarion Partners Partnership
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																1,557	1,423
Our share of gain on sale of real estate																$ 0	$ 4,401

[1] (1)First quarter 2016 includes a $25.7 million gain on change in control of interests from our Clarion Partners acquisition as further discussed in Note 3. Third quarter 2016 includes a $4.9 million gain on sale from the reversal of our warranty reserve on condominiums sold at Santana Row as further discussed in Note 9. 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.