Selected Quarterly Financial Data (Unaudited) Summary Of Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 239,149		$ 233,947		$ 230,465		$ 232,227		$ 235,376		$ 229,753		$ 224,902		$ 225,405		$ 935,788	$ 915,436	$ 857,348
Operating income	176,221	[1]	94,018	[1]	109,579	[1]	91,093	[1]	84,840	[2]	93,467	[2]	93,868	[2]	89,461	[2]	470,911	361,636	410,210
Net income	148,966	[1]	67,106	[1]	82,667	[1]	61,803	[1]	56,382	[2]	64,180	[2]	65,533	[2]	62,931	[2]	360,542	249,026	297,870
Net income attributable to the Trust	147,355	[1]	65,465	[1]	80,902	[1]	60,144	[1]	54,507	[2]	62,558	[2]	63,595	[2]	61,247	[2]	353,866	241,907	289,914
Net income available for common shareholders	$ 145,344	[1]	$ 63,455	[1]	$ 78,891	[1]	$ 58,134	[1]	$ 52,496	[2]	$ 60,548	[2]	$ 61,584	[2]	$ 59,237	[2]	$ 345,824	$ 233,865	$ 287,456
Earnings Per Common Share, Basic	$ 1.92	[1]	$ 0.84	[1]	$ 1.05	[1]	$ 0.78	[1]	$ 0.71	[2]	$ 0.82	[2]	$ 0.84	[2]	$ 0.81	[2]	$ 4.61	$ 3.18	$ 3.97
Earnings Per Common Share, Diluted	$ 1.92	[1]	$ 0.84	[1]	$ 1.05	[1]	$ 0.78	[1]	$ 0.71	[2]	$ 0.82	[2]	$ 0.84	[2]	$ 0.81	[2]	$ 4.61	$ 3.18	$ 3.97

[1] Second and third quarter 2019 include net gains of $16.2 million and $14.3 million, respectively, related to the sale of two properties and one parcel of land, as well as condominiums sold at our Assembly Row and Pike & Rose properties. Third quarter 2019 also includes an $11.9 million charge related to the buyout of a lease at Assembly Square Marketplace. Fourth quarter 2019 includes an $85.1 million net gain on sale under the threat of condemnation of a portion of San Antonio Center. All of these transactions are further discussed in Note 3.

[2] First and second quarter 2018 include net gains of $3.3 million and $4.0 million, respectively, related to condominiums sold at our Assembly Row and Pike & Rose properties. Third and fourth quarter 2018 include gains of $3.1 million and $1.6 million, respectively, related to the sale of one residential building and one property. All of these transactions are further discussed in Note 3.