Subsequent Event - Additional Information (Detail) - Senior Unsecured Notes Due in 2026 [Member] - Subsequent Event [Member] - Confirmation of Acceptance [Member] - MetLife Investment Advisors, LLC and Certain of Its Affiliates [Member]	Feb. 05, 2019 USD ($)
Subsequent Event [Line Items]
Senior notes, face amount	$ 100,000,000
Debt instrument, interest rate	3.93%
Maturity date of debt instruments	Oct. 10, 2026
Debt instrument, frequency of periodic payment	quarterly
Aggregate maximum additional borrowing capacity	$ 200,000,000