Derivative Instruments - Schedule of Derivative Instruments Reported in Financial Position (Detail) - Derivatives Not Designated as Hedging Instruments $ in Thousands	Mar. 31, 2020 USD ($) derivative	Dec. 31, 2019 USD ($) derivative
Equity-indexed options | Other invested assets
Derivatives, Fair Value [Line Items]
Number of Instruments | derivative	466	473
Notional Amount, assets	$ 2,669,500	$ 2,654,600
Estimated Fair Value, assets	$ 125,988	$ 256,005
Equity-indexed embedded derivative | Policyholders’ account balances
Derivatives, Fair Value [Line Items]
Number of Instruments | derivative	103,593	101,950
Notional Amount, liabilities	$ 2,545,271	$ 2,527,205
Estimated Fair Value, liabilities	$ 630,952	$ 731,552