Concentration Risk (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) tenant	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) tenant	Sep. 30, 2016 USD ($)
Concentration Risk
Number of significant tenants | tenant	1		1
Rental income	$ 11,107	$ 6,164	$ 28,381	$ 16,462
Approximate total acres | Geographic concentration
Concentration Risk
Concentration risk (as a percent)			100.00%	100.00%
Approximate total acres | Geographic concentration | Corn belt
Concentration Risk
Concentration risk (as a percent)			30.80%	29.30%
Approximate total acres | Geographic concentration | Delta and South
Concentration Risk
Concentration risk (as a percent)			18.80%	21.80%
Approximate total acres | Geographic concentration | High Plains
Concentration Risk
Concentration risk (as a percent)			20.40%	24.10%
Approximate total acres | Geographic concentration | Southeast
Concentration Risk
Concentration risk (as a percent)			25.80%	24.80%
Approximate total acres | Geographic concentration | West Coast
Concentration Risk
Concentration risk (as a percent)			4.20%
Rental income | Tenant concentration | Tenant A
Concentration Risk
Rental income	$ 2,091		$ 4,071
Concentration risk (as a percent)	18.80%		14.30%
Rental income | Geographic concentration
Concentration Risk
Concentration risk (as a percent)	100.00%	100.00%	100.00%	100.00%
Rental income | Geographic concentration | Corn belt
Concentration Risk
Concentration risk (as a percent)	33.70%	40.20%	35.50%	37.50%
Rental income | Geographic concentration | Delta and South
Concentration Risk
Concentration risk (as a percent)	9.30%	11.40%	10.00%	11.70%
Rental income | Geographic concentration | High Plains
Concentration Risk
Concentration risk (as a percent)	8.60%	15.80%	9.30%	15.60%
Rental income | Geographic concentration | Southeast
Concentration Risk
Concentration risk (as a percent)	18.30%	32.60%	21.20%	35.20%
Rental income | Geographic concentration | West Coast
Concentration Risk
Concentration risk (as a percent)	30.10%		24.00%