Pension and Other Postretirement Plans - Defined Contribution Pension Plans (Details) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
National Western Life Insurance Company:
Defined Benefit Plan Disclosure [Line Items]
Additional company's matching contribution		4.00%	4.00%	4.00%
Non-Qualified Contribution Pension Plan | National Western Life Insurance Company:
Defined Benefit Plan Disclosure [Line Items]
Total company contribution, non-qualified deferred compensation		$ 175	$ 97	$ 127
Non-Qualified Contribution Pension Plan | Ozark National Life Insurance Company:
Defined Benefit Plan Disclosure [Line Items]
Total company contribution, non-qualified deferred compensation	$ 45	247
United States | Qualified Plan | National Western Life Insurance Company:
Defined Benefit Plan Disclosure [Line Items]
Total company contribution, 401(k) plan		720	$ 664	$ 615
United States | Qualified Plan | Ozark National Life Insurance Company:
Defined Benefit Plan Disclosure [Line Items]
Total company contribution, 401(k) plan	176	175
United States | Qualified Plan | NIS
Defined Benefit Plan Disclosure [Line Items]
Total company contribution, 401(k) plan	$ 30	$ 17