Quarterly report pursuant to Section 13 or 15(d)

Borrowings - Additional Information (Detail)

v3.8.0.1
Borrowings - Additional Information (Detail)
3 Months Ended
Mar. 31, 2018
USD ($)
debt_instrument
Mar. 31, 2017
Mar. 13, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 15, 2017
May 31, 2017
USD ($)
debt_instrument
Jun. 16, 2016
USD ($)
Debt Instrument [Line Items]              
Weighted average interest rate (as percent) 3.52% 3.25%          
Borrowings under lines of credit $ 3,900,000     $ 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            
Revolving equity lines of credit borrowing capacity 75,000,000            
New MetLife Facility | Notes and bonds payables              
Debt Instrument [Line Items]              
Face amount of debt 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            
Farmer Mac Bonds Payable, 2017 Issuances              
Debt Instrument [Line Items]              
Face amount of debt     $ 1,300,000        
Number of debt instruments | debt_instrument 1            
Mortgage notes and bonds payable | Notes and bonds payables              
Debt Instrument [Line Items]              
Aggregate fair value of mortgage notes payable outstanding $ 278,800,000            
Mortgage notes payable, carrying value 291,100,000            
Short-term variable-rate mortgage notes and bonds payable | Notes and bonds payables              
Debt Instrument [Line Items]              
Borrowings under lines of credit $ 3,900,000            
Maximum | New MetLife Facility              
Debt Instrument [Line Items]              
Debt fee percentage         0.20%    
Minimum | New MetLife Facility              
Debt Instrument [Line Items]              
Debt fee percentage 0.10%