Concentration Risk (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Concentration Risk        
Rental income $ 10,471 $ 5,881 $ 17,274 $ 10,298
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% 30.20%
Approximate total acres | Geographic concentration | Delta and South        
Concentration Risk        
Concentration risk (as a percent)     18.80% 22.40%
Approximate total acres | Geographic concentration | High Plains        
Concentration Risk        
Concentration risk (as a percent)     20.40% 24.60%
Approximate total acres | Geographic concentration | Southeast        
Concentration Risk        
Concentration risk (as a percent)     25.80% 22.80%
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 $ 1,201   $ 1,978  
Concentration risk (as a percent) 11.30%   11.50%  
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) 32.70% 41.20% 36.70% 35.90%
Rental income | Geographic concentration | Delta and South        
Concentration Risk        
Concentration risk (as a percent) 14.20% 12.00% 13.30% 11.90%
Rental income | Geographic concentration | High Plains        
Concentration Risk        
Concentration risk (as a percent) 8.90% 14.00% 9.70% 15.40%
Rental income | Geographic concentration | Southeast        
Concentration Risk        
Concentration risk (as a percent) 22.30% 32.80% 20.20% 36.80%
Rental income | Geographic concentration | West Coast        
Concentration Risk        
Concentration risk (as a percent) 21.90%   20.10%