Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	Jan. 15, 2016 $ / shares	Mar. 31, 2016 USD ($) item	Feb. 29, 2016 USD ($) ft² item	Jan. 31, 2016 USD ($) ft²	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares
Subsequent Events
Dividend or distribution paid | $ / shares					$ 0.9300	$ 0.9000
Acquisition price					$ 82,586	$ 132,990
Subsequent Event
Subsequent Events
Dividend or distribution paid | $ / shares	$ 0.2325
Operating Partnership
Subsequent Events
Dividend or distribution paid | $ / shares					$ 0.9300	$ 0.9000
Specific Implement Dealership, North Platte, NE | Operating Partnership | Subsequent Event
Subsequent Events
Area of the property purchased | ft²				19,595
Acquisition price				$ 1,769
Specific Apartment 72 Unit and Townhome 8 Unit, Complex, Grand Forks, ND | Operating Partnership | Subsequent Event
Subsequent Events
Number of apartment units acquired | item			72
Number of townhome units acquired | item			8
Acquisition price			$ 5,050
Specific Office Building, White Bear Lake, MN | Operating Partnership | Subsequent Event
Subsequent Events
Area of the property purchased | ft²			25,817
Acquisition price			$ 4,000
Specific Apartment Complex One, 20 Unit, Bismarck, ND | Operating Partnership | Subsequent Event
Subsequent Events
Number of apartment units acquired | item		20
Acquisition price		$ 1,550
Specific Apartment Complex Two, 20 Unit, Bismarck, ND | Operating Partnership | Subsequent Event
Subsequent Events
Number of apartment units acquired | item		20
Acquisition price		$ 1,550