Derivative Instruments - Schedule of Derivative Instruments Reported in Financial Position (Detail) - Derivatives Not Designated as Hedging Instruments $ in Thousands	Dec. 31, 2019 USD ($) derivative	Dec. 31, 2018 USD ($) derivative
Equity-Indexed Options | Other Invested Assets
Derivatives, Fair Value [Line Items]
Number of instruments | derivative	473	493
Notional amount, asset	$ 2,654,600	$ 2,391,000
Estimated fair value, assets	$ 256,005	$ 148,006
Equity-Indexed Embedded Derivative | Policyholders' Account Balances
Derivatives, Fair Value [Line Items]
Number of instruments | derivative	101,950	90,440
Notional amount, liability	$ 2,527,205	$ 2,327,769
Estimated fair value, liabilities	$ 731,552	$ 596,075