Investments - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Debt Securities Available-for-Sale (Parenthetical) (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Two Thousand And Eighteen Advance Agreement [Member]
Debt Securities, Available-for-Sale [Line Items]
Carrying amount	$ 23.6	$ 26.3
Two Thousand And Twenty Four Advance Agreement [Member]
Debt Securities, Available-for-Sale [Line Items]
Carrying amount	$ 19.8