Fair Value Valuation of Financial Instruments Not Reported at Fair Value by Hierarchy Level (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans	$ 1,011,678	$ 1,039,829
Policy loans	201,589	197,366
Other investments	34,181	5,757
Supplementary contracts without life contingencies	296,915	303,627
Liabilities related to separate accounts	645,881	561,281
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Assets, Fair Value Disclosure	696,871	609,207
Future policy benefits	0	0
Liabilities, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	31,469	4,745
Assets, Fair Value Disclosure	7,770,353	7,013,911
Future policy benefits	0	0
Liabilities, Fair Value Disclosure	254	780
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Assets, Fair Value Disclosure	36,050	100,414
Liabilities, Fair Value Disclosure	76,346	40,028
Portion at Other than Fair Value Measurement | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans	1,059,073	1,045,497
Policy loans	256,787	237,496
Other investments	31,749	30,087
Assets, Fair Value Disclosure	1,347,609	1,313,080
Future policy benefits	4,381,863	3,981,947
Supplementary contracts without life contingencies	309,601	298,869
Advance premiums and other deposits	245,480	252,318
Long-term debt	84,438	65,999
Liabilities related to separate accounts	644,691	559,799
Liabilities, Fair Value Disclosure	5,666,073	5,158,932
Portion at Other than Fair Value Measurement | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans	0	0
Policy loans	0	0
Other investments	0	0
Assets, Fair Value Disclosure	0	0
Future policy benefits	0	0
Supplementary contracts without life contingencies	0	0
Advance premiums and other deposits	0	0
Long-term debt	0	0
Liabilities related to separate accounts	0	0
Liabilities, Fair Value Disclosure	0	0
Portion at Other than Fair Value Measurement | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans	0	0
Policy loans	0	0
Other investments	29,534	0
Assets, Fair Value Disclosure	29,534	0
Future policy benefits	0	0
Supplementary contracts without life contingencies	0	0
Advance premiums and other deposits	0	0
Long-term debt	0	0
Liabilities related to separate accounts	0	0
Liabilities, Fair Value Disclosure	0	0
Portion at Other than Fair Value Measurement | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans	1,059,073	1,045,497
Policy loans	256,787	237,496
Other investments	2,215	30,087
Assets, Fair Value Disclosure	1,318,075	1,313,080
Future policy benefits	4,381,863	3,981,947
Supplementary contracts without life contingencies	309,601	298,869
Advance premiums and other deposits	245,480	252,318
Long-term debt	84,438	65,999
Liabilities related to separate accounts	644,691	559,799
Liabilities, Fair Value Disclosure	5,666,073	5,158,932
Reported Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans	1,011,678	1,039,829
Policy loans	201,589	197,366
Other investments	31,211	29,020
Assets not measured at fair value	1,244,478	1,266,215
Future policy benefits	4,270,073	4,217,904
Supplementary contracts without life contingencies	296,915	303,627
Advance premiums and other deposits	245,480	252,318
Long-term debt	97,000	97,000
Liabilities related to separate accounts		561,281
Liabilities not measured at fair value	$ 5,555,349	$ 5,432,130