Investments - Schedule of Components of Net Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	$ 348,518	$ 404,860	$ 435,537
Less investment expenses	2,762	2,412	3,252
Net investment income (excluding derivatives and trading securities)	345,756	402,448	432,285
Net investment income	562,530	417,202	555,492
Debt and equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	309,082	373,479	403,372
Mortgage loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	20,155	13,162	12,595
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	2,667	3,361	3,539
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	293	2,160	2,974
Other investment assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	16,321	12,698	13,057
Index option derivative gain
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Index option derivative gain	120,718	14,754	123,207
Embedded derivative on reinsurance
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	84,725	0	0
Trading securities market adjustments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 11,331	$ 0	$ 0