Business Segments - Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue:
Premium	$ 4,302,709	$ 4,099,887	$ 3,813,905
Net investment income	987,499	952,447	927,062
Other income	1,246	1,216	1,325
Total revenue	5,291,454	5,053,550	4,742,292
Expenses:
Policy obligations	2,865,456	2,859,616	2,572,884
Required interest on reserves	0	0	0
Required interest on DAC	0	0	0
Amortization of acquisition costs	624,407	603,838	575,770
Commissions, premium taxes, and non-deferred acquisition costs	374,383	331,510	304,841
Insurance administrative expense	307,516	282,029	254,932
Parent expense	10,788	9,728	10,214
Stock-based compensation expense	35,650	30,272	35,892
Interest expense	90,395	83,486	86,704
Total benefits and expenses	4,308,595	4,200,479	3,841,237
Subtotal	982,859	853,071	901,055
Non-operating items	7,807	11,898	4,308
Measure of segment profitability (pretax)	990,666	864,969	905,363
Realized gain (loss)—investments	(76,548)	68,633	(3,737)
Realized loss—redemption of debt	0	(9,314)	(634)
Administrative settlements		(1,325)
Legal proceedings	(2,496)	(8,139)	(3,275)
Non-operating expenses	(5,311)	(2,434)	(1,033)
Income before income taxes	906,311	912,390	896,684
Life
Revenue:
Premium	3,023,296	2,898,210	2,672,804
Health
Revenue:
Premium	1,279,412	1,201,676	1,141,097
Annuity
Revenue:
Premium	1	1	4
Operating Segments
Expenses:
Non-operating items	0	0
Operating Segments | Life
Revenue:
Premium	3,023,296	2,898,210	2,672,804
Net investment income	0	0	0
Other income	0	0	0
Total revenue	3,023,296	2,898,210	2,672,804
Expenses:
Policy obligations	2,045,730	2,070,485	1,809,373
Required interest on reserves	(771,914)	(735,282)	(698,112)
Required interest on DAC	229,957	218,575	210,152
Amortization of acquisition costs	494,431	486,724	463,586
Commissions, premium taxes, and non-deferred acquisition costs	256,546	234,033	212,859
Insurance administrative expense	0	0	0
Parent expense	0	0	0
Stock-based compensation expense	0	0	0
Interest expense	0	0	0
Total benefits and expenses	2,254,750	2,274,535	1,997,858
Subtotal	768,546	623,675	674,946
Non-operating items			0
Measure of segment profitability (pretax)	768,546	623,675	674,946
Operating Segments | Health
Revenue:
Premium	1,279,412	1,201,676	1,141,097
Net investment income	0	0	0
Other income	0	0	0
Total revenue	1,279,412	1,201,676	1,141,097
Expenses:
Policy obligations	791,809	758,745	733,481
Required interest on reserves	(109,789)	(102,574)	(93,475)
Required interest on DAC	30,695	28,556	26,586
Amortization of acquisition costs	128,170	115,194	110,177
Commissions, premium taxes, and non-deferred acquisition costs	117,815	97,453	91,959
Insurance administrative expense	0	0	0
Parent expense	0	0	0
Stock-based compensation expense	0	0	0
Interest expense	0	0	0
Total benefits and expenses	958,700	897,374	868,728
Subtotal	320,712	304,302	272,369
Non-operating items			0
Measure of segment profitability (pretax)	320,712	304,302	272,369
Operating Segments | Annuity
Revenue:
Premium	1	1	4
Net investment income	0	0	0
Other income	0	0	0
Total revenue	1	1	4
Expenses:
Policy obligations	27,846	29,061	30,030
Required interest on reserves	(38,090)	(39,966)	(41,413)
Required interest on DAC	191	258	328
Amortization of acquisition costs	1,806	1,920	2,007
Commissions, premium taxes, and non-deferred acquisition costs	22	24	23
Insurance administrative expense	0	0	0
Parent expense	0	0	0
Stock-based compensation expense	0	0	0
Interest expense	0	0	0
Total benefits and expenses	(8,225)	(8,703)	(9,025)
Subtotal	8,226	8,704	9,029
Non-operating items			0
Measure of segment profitability (pretax)	8,226	8,704	9,029
Operating Segments | Investment
Revenue:
Premium	0	0	0
Net investment income	987,499	952,447	927,062
Other income	0	0	0
Total revenue	987,499	952,447	927,062
Expenses:
Policy obligations	71	0	0
Required interest on reserves	919,793	877,822	833,000
Required interest on DAC	(260,843)	(247,389)	(237,066)
Amortization of acquisition costs	0	0	0
Commissions, premium taxes, and non-deferred acquisition costs	0	0	0
Insurance administrative expense	0	0	0
Parent expense	0	0	0
Stock-based compensation expense	0	0	0
Interest expense	90,395	83,486	86,704
Total benefits and expenses	749,416	713,919	682,638
Subtotal	238,083	238,528	244,424
Non-operating items			0
Measure of segment profitability (pretax)	238,083	238,528	244,424
Corporate & Other
Revenue:
Premium	0	0	0
Net investment income	0	0	0
Other income	1,246	1,216	1,325
Total revenue	1,246	1,216	1,325
Expenses:
Policy obligations	0	0	0
Required interest on reserves	0	0	0
Required interest on DAC	0	0	0
Amortization of acquisition costs	0	0	0
Commissions, premium taxes, and non-deferred acquisition costs	0	0	0
Insurance administrative expense	299,341	271,631	250,947
Parent expense	11,156	9,553	9,891
Stock-based compensation expense	35,650	30,272	35,892
Interest expense	0	0	0
Total benefits and expenses	346,147	311,456	296,730
Subtotal	(344,901)	(310,240)	(295,405)
Non-operating items	0	0	0
Measure of segment profitability (pretax)	(344,901)	(310,240)	(295,405)
Adjustments
Revenue:
Premium	0	0	0
Net investment income	0	0	0
Other income	0	0	0
Total revenue	0	0	0
Expenses:
Policy obligations	0	1,325	0
Required interest on reserves	0	0	0
Required interest on DAC	0	0	0
Amortization of acquisition costs	0	0	0
Commissions, premium taxes, and non-deferred acquisition costs	0	0	0
Insurance administrative expense	8,175	10,398	3,985
Parent expense	(368)	175	323
Stock-based compensation expense	0	0	0
Interest expense	0	0	0
Total benefits and expenses	7,807	11,898	4,308
Subtotal	(7,807)	(11,898)	(4,308)
Non-operating items	7,807	11,898	4,308
Measure of segment profitability (pretax)	$ 0	$ 0	$ 0