Real Estate (Real Estate and Accumulated Depreciation) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cost
Balance, beginning of year		$ 1,515,206,000	$ 1,508,682,000
Properties transferred to held for sale		(22,512,000)	(36,265,000)	$ (61,505,000)
Property acquisitions			9,333,000	6,481,000
Outparcel dispositions		(840,000)
Asset write-offs			(3,633,000)
Improvements and betterments		35,624,000	37,089,000	29,107,000
Balance, end of the year		1,527,478,000	1,515,206,000	1,508,682,000
Accumulated depreciation
Balance, beginning of the year		389,861,000	361,969,000
Properties transferred held for sale		(3,947,000)	(10,143,000)	(14,886,000)
Outparcel dispositions		(90,000)
Asset write-offs			(3,107,000)
Depreciation expense	[1]	42,745,000	41,142,000	34,912,000
Balance, end of the year		428,569,000	389,861,000	361,969,000
Net book value		$ 1,098,909,000	$ 1,125,345,000	$ 1,146,713,000

[1] Depreciation is provided over the estimated useful lives of the buildings and improvements, which range from 3 to 40 years.