Annual report pursuant to Section 13 and 15(d)

Borrowings - Terms of MetLife Facility (Detail)

v3.10.0.1
Borrowings - Terms of MetLife Facility (Detail) - MetLife Credit Facility - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2018
Debt Instrument [Line Items]    
Aggregate Commitment   $ 200,000,000
Principal Outstanding   126,758,000
Long-term debt, additional amount available   $ 18,100,000
Minimum annualized rate (as percent)   2.50%
Minimum    
Debt Instrument [Line Items]    
Commitment fee (as percent)   0.10%
Unused fee (as percent)   0.10%
Maximum    
Debt Instrument [Line Items]    
Commitment fee (as percent)   0.20%
Unused fee (as percent) 0.20%  
Notes payable to bank    
Debt Instrument [Line Items]    
Aggregate Commitment   $ 200,000,000
Principal Outstanding   $ 126,658,000
Weighted-average interest rate (as percent)   3.30%
Term of debt   9 years
Undrawn Commitment   $ 63,530,000
Line of credit    
Debt Instrument [Line Items]    
Aggregate Commitment   75,000,000
Principal Outstanding   100,000
Undrawn Commitment   $ 74,900,000
Interest rate (as percent)   4.66%
Line of credit | LIBOR    
Debt Instrument [Line Items]    
Basis spread (as percent)   2.25%