Principal Activity and Significant Accounting Policies - Principal Business Activity (Details) $ in Thousands	Jun. 30, 2020 USD ($) ft² property item	Dec. 31, 2019 USD ($)
Properties
Real estate investments | $	$ 671,477	$ 655,712
No. of properties	177
Residential Property
Properties
Percentage of residential property out of the trust properties	74.20%
No. of properties	131
Units | item	10,040
Residential Property | North Dakota
Properties
No. of properties	111
Units | item	6,348
Residential Property | Minnesota
Properties
No. of properties	16
Units | item	3,033
Residential Property | Missouri
Properties
No. of properties	1
Units | ft²	164
Residential Property | Nebraska
Properties
No. of properties	3
Units | item	495
Commercial Property
Properties
Percentage of commercial property out of the trust properties	25.80%
No. of properties	46
Area of commercial property | ft²	1,646,000
Commercial Property | North Dakota
Properties
No. of properties	20
Area of commercial property | ft²	780,000
Commercial Property | Minnesota
Properties
No. of properties	13
Area of commercial property | ft²	664,000
Commercial Property | Nebraska
Properties
No. of properties	1
Area of commercial property | ft²	19,000
Commercial Property | Arkansas
Properties
No. of properties	2
Area of commercial property | ft²	28,000
Commercial Property | Colorado
Properties
No. of properties	1
Area of commercial property | ft²	17,000
Commercial Property | Iowa
Properties
No. of properties	1
Area of commercial property | ft²	33,000
Commercial Property | Louisiana
Properties
No. of properties	1
Area of commercial property | ft²	15,000
Commercial Property | Michigan
Properties
No. of properties	1
Area of commercial property | ft²	12,000
Commercial Property | Mississippi
Properties
No. of properties	1
Area of commercial property | ft²	15,000
Commercial Property | Wisconsin
Properties
No. of properties	5
Area of commercial property | ft²	63,000