Derivative Instruments - Schedule of Derivative Instruments Reported in Statements of Operations (Detail) - Derivatives Not Designated as Hedging Instruments - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Investment Income | Equity-Indexed Options
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in income on derivatives	$ 144,980	$ (54,951)	$ 91,055
Interest Credited to Policyholders' Account Balances | Equity-Indexed Embedded Derivative
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in income on derivatives	$ (162,011)	$ 17,862	$ (98,351)