Quarterly report pursuant to Section 13 or 15(d)

Borrowings - Additional Information (Detail)

v3.10.0.1
Borrowings - Additional Information (Detail)
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
debt_instrument
Jun. 30, 2017
Jun. 30, 2018
USD ($)
debt_instrument
Jun. 30, 2017
Mar. 13, 2018
USD ($)
Dec. 31, 2017
USD ($)
May 31, 2017
USD ($)
debt_instrument
Dec. 05, 2014
USD ($)
Debt Instrument [Line Items]                
Weighted average interest rate (as percent) 3.60% 3.28% 3.56% 3.27%        
Borrowings under lines of credit $ 3,500,000   $ 3,500,000     $ 10,000,000    
Metlife Term Loans | Notes and bonds payables                
Debt Instrument [Line Items]                
Face amount of debt             $ 15,032,000  
Number of debt instruments | debt_instrument             2  
MetLife Facility                
Debt Instrument [Line Items]                
Face amount of debt 200,000,000   200,000,000          
Revolving equity lines of credit borrowing capacity 75,000,000   75,000,000          
New MetLife Facility | Notes and bonds payables                
Debt Instrument [Line Items]                
Face amount of debt $ 200,000,000   $ 200,000,000          
Farmer Mac Bonds Payable                
Debt Instrument [Line Items]                
Face amount of debt         $ 125,000,000     $ 125,000,000
Number of debt instruments | debt_instrument 15   15          
Farmer Mac Bonds Payable, 2017 Issuances                
Debt Instrument [Line Items]                
Face amount of debt         $ 1,260,000      
Number of debt instruments | debt_instrument 1   1          
Mortgage notes and bonds payable | Notes and bonds payables                
Debt Instrument [Line Items]                
Aggregate fair value of mortgage notes payable outstanding $ 278,000,000   $ 278,000,000          
Mortgage notes payable, carrying value 291,900,000   291,900,000          
Short-term variable-rate mortgage notes and bonds payable | Notes and bonds payables                
Debt Instrument [Line Items]                
Borrowings under lines of credit $ 3,500,000   $ 3,500,000