Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2020	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in future policy benefits liability				$ 15,000
Decrease to deferred federal income tax liability		$ (101,166)	$ (145,126)
Revised beginning balance		(2,281,986)	(2,102,577)
Derivatives, index options		101,622	132,821
Unrealized gains (losses) on options held		120,717	14,754	123,207
Embedded derivative, fair value		84,700	0
Cost of reinsurance		89,686	102,840	0		$ 0
Ceding commission paid			48,000
Carrying value of capitalized software, property and equipment		165,300	155,900
Accumulated depreciation and amortization		84,000	72,600
Depreciation and amortization expense		13,000	11,900	10,700
Goodwill		13,864	13,864	13,864
Identifiable intangible assets acquired in business combination		7,500	8,200
Mortgage loans-allowance for possible losses		2,987	2,486
Debt securities held to maturity, allowance for credit losses		0	0	0
Stockholders' equity		2,539,691	2,539,750	2,116,430
Retained earnings:
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity		$ 2,281,986	2,102,577	2,014,570
Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in future policy benefits liability				15,000
Decrease to deferred federal income tax liability				3,200
Revised beginning balance				11,800
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revised beginning balance					$ (3,000)
Mortgage loans-allowance for possible losses					1,200
Debt securities held to maturity, allowance for credit losses				3,334	$ 3,300
Cumulative Effect, Period of Adoption, Adjustment | Retained earnings:
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity	[1]		0	$ (3,032)		$ 0
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of assets		3 years
Interest rate range to calculate future mortality		3.25%
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of assets		39 years
Interest rate range to calculate future mortality		8.00%
Options Held
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unrealized gains (losses) on options held		$ 54,400	$ 71,000

[1] The 2019 beginning balance was revised by $11.8 million.