Principal Activity and Significant Accounting Policies - Principal Business Activity (Details)	Dec. 31, 2016 ft² property item
Properties
No. of properties	155
Residential Property
Properties
No. of properties	105
Percentage of residential property out of the trust properties	69.40%
Units | item	8,991
Residential Property | North Dakota
Properties
No. of properties	86
Units | item	5,484
Residential Property | Minnesota
Properties
No. of properties	16
Units | item	3,027
Residential Property | Missouri
Properties
No. of properties	1
Area of commercial property | ft²	164
Residential Property | Nebraska
Properties
No. of properties	2
Units | item	316
Commercial Property
Properties
No. of properties	50
Percentage of commercial property out of the trust properties	30.60%
Area of commercial property | ft²	1,719,211
Commercial Property | North Dakota
Properties
No. of properties	21
Area of commercial property | ft²	832,920
Commercial Property | Arkansas
Properties
No. of properties	2
Area of commercial property | ft²	29,370
Commercial Property | Colorado
Properties
No. of properties	1
Area of commercial property | ft²	13,390
Commercial Property | Iowa
Properties
No. of properties	1
Area of commercial property | ft²	32,532
Commercial Property | Louisiana
Properties
No. of properties	1
Area of commercial property | ft²	14,560
Commercial Property | Michigan
Properties
No. of properties	1
Area of commercial property | ft²	11,737
Commercial Property | Minnesota
Properties
No. of properties	15
Area of commercial property | ft²	683,090
Commercial Property | Mississippi
Properties
No. of properties	1
Area of commercial property | ft²	14,820
Commercial Property | Nebraska
Properties
No. of properties	1
Area of commercial property | ft²	16,480
Commercial Property | Texas
Properties
No. of properties	1
Area of commercial property | ft²	7,296
Commercial Property | Wisconsin
Properties
No. of properties	5
Area of commercial property | ft²	63,016