Investments - Narrative (Details) $ in Thousands		3 Months Ended			12 Months Ended
	Dec. 31, 2020 USD ($) loan	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 30, 2020 USD ($)	Jan. 31, 2019 USD ($)
Schedule of Investments [Line Items]
Loans originated during the year					$ 80,200	$ 121,400
Net investments in mortgage loans, after allowances for possible losses	$ 332,521				332,521	272,422
Mortgage loans-allowance for possible losses	2,486				2,486	675
Increase (decrease) to retained earnings	2,102,577				2,102,577	2,014,570
Real estate investments	104,113				104,113	62,090
Real estate gain (loss)					2,661	6,911	$ 1,799
Debt securities, available-for-sale	10,770,923				10,770,923	3,356,945
Realized gains on investments					21,071	6,241	8,423
Debt securities, held to maturity						7,106,245
Securities, other-than-temporarily impaired						7,800
Debt securities held to maturity, fair value	0				0	7,407,703
Transfer, fair value	7,300,000				7,300,000
Transfer, amortized cost	6,700,000				6,700,000
Gross Unrealized Gains	$ 600,000				$ 600,000	303,060
Loans In Forbearance
Schedule of Investments [Line Items]
Number of loans | loan	1				8
Loans receivable	$ 4,700				$ 4,700			$ 29,200
Cumulative Effect, Period of Adoption, Adjustment
Schedule of Investments [Line Items]
Mortgage loans-allowance for possible losses						1,200
Increase (decrease) to retained earnings						3,000
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Schedule of Investments [Line Items]
Increase (decrease) to retained earnings						400
Real Estate
Schedule of Investments [Line Items]
Real estate investments	33,800				33,800	34,600
Operating income recognized on real estate investment properties					2,900	2,900	2,200
Debt Securities
Schedule of Investments [Line Items]
Realized gains on investments					21,100	6,200	8,400
External Credit Rating, Non Investment Grade | Debt Securities
Schedule of Investments [Line Items]
Debt securities, available-for-sale	$ 303,500				$ 303,500	$ 83,700
Debt securities below investment grade, percentage of total invested assets	2.70%				2.70%	0.80%
Non- Income Producing
Schedule of Investments [Line Items]
Real estate investment	$ 400				$ 400	$ 400	$ 5,200
Nursing Home Operations in Reno, Nevada
Schedule of Investments [Line Items]
Real estate gain (loss)				$ 5,700
Nursing Home Operations, San Marcos, Texas
Schedule of Investments [Line Items]
Real estate gain (loss)			$ (2,000)
Prior Home Office
Schedule of Investments [Line Items]
Real estate gain (loss)		$ 3,200
Ozark National Life Insurance Company:
Schedule of Investments [Line Items]
Debt securities, available-for-sale	811,600				811,600	415,700
Debt securities, held to maturity	$ 0				0	$ 307,200
Ozark National Life Insurance Company: | Real Estate
Schedule of Investments [Line Items]
Real estate investments									$ 4,300
Travis County
Schedule of Investments [Line Items]
Gain on sale of property					$ 2,700