Business Segments - Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenue:
Premium	$ 1,095,090	$ 1,064,812
Net investment income	257,105	244,894
Other income	50	164
Total revenue	1,352,245	1,309,870
Expenses:
Policy obligations	707,927	694,149
Required interest on reserves	0	0
Amortization of acquisition costs	92,322	84,496
Commissions, premium taxes, and non-deferred acquisition costs	137,797	125,509
Insurance administrative expense	73,907	72,677
Parent expense	2,585	2,640
Stock-based compensation expense	7,679	9,035
Interest expense	24,867	19,944
Total benefits and expenses	1,047,084	1,008,450
Subtotal	305,161	301,420
Non-operating items	0	112
Measure of segment profitability (pretax)	305,161	301,532
Realized gain (loss)—investments	(30,927)	(7,244)
Non-operating expenses		(112)
Income before income taxes	274,234	294,176
Life
Revenue:
Premium	772,597	749,128
Expenses:
Amortization of acquisition costs	79,589	71,929
Health
Revenue:
Premium	322,493	315,684
Expenses:
Amortization of acquisition costs	12,308	12,114
Annuity
Revenue:
Premium	0	0
Operating Segments
Expenses:
Non-operating items	0	0
Operating Segments | Life
Revenue:
Premium	772,597	749,128
Net investment income	0	0
Other income	0	0
Total revenue	772,597	749,128
Expenses:
Policy obligations	507,977	495,429
Required interest on reserves	(189,821)	(181,372)
Amortization of acquisition costs	79,589	71,929
Commissions, premium taxes, and non-deferred acquisition costs	83,578	73,548
Insurance administrative expense	0	0
Parent expense	0	0
Stock-based compensation expense	0	0
Interest expense	0	0
Total benefits and expenses	481,323	459,534
Subtotal	291,274	289,594
Measure of segment profitability (pretax)	291,274	289,594
Operating Segments | Health
Revenue:
Premium	322,493	315,684
Net investment income	0	0
Other income	0	0
Total revenue	322,493	315,684
Expenses:
Policy obligations	190,962	189,018
Required interest on reserves	(26,323)	(25,270)
Amortization of acquisition costs	12,308	12,114
Commissions, premium taxes, and non-deferred acquisition costs	54,214	51,952
Insurance administrative expense	0	0
Parent expense	0	0
Stock-based compensation expense	0	0
Interest expense	0	0
Total benefits and expenses	231,161	227,814
Subtotal	91,332	87,870
Measure of segment profitability (pretax)	91,332	87,870
Operating Segments | Annuity
Revenue:
Premium	0	0
Net investment income	0	0
Other income	0	0
Total revenue	0	0
Expenses:
Policy obligations	7,541	8,642
Required interest on reserves	(10,259)	(11,367)
Amortization of acquisition costs	425	453
Commissions, premium taxes, and non-deferred acquisition costs	5	9
Insurance administrative expense	0	0
Parent expense	0	0
Stock-based compensation expense	0	0
Interest expense	0	0
Total benefits and expenses	(2,288)	(2,263)
Subtotal	2,288	2,263
Measure of segment profitability (pretax)	2,288	2,263
Operating Segments | Investment
Revenue:
Premium	0	0
Net investment income	257,105	244,894
Other income	0	0
Total revenue	257,105	244,894
Expenses:
Policy obligations	1,447	1,060
Required interest on reserves	226,403	218,009
Amortization of acquisition costs	0	0
Commissions, premium taxes, and non-deferred acquisition costs	0	0
Insurance administrative expense	0	0
Parent expense	0	0
Stock-based compensation expense	0	0
Interest expense	0	0
Total benefits and expenses	227,850	219,069
Subtotal	29,255	25,825
Measure of segment profitability (pretax)	29,255	25,825
Corporate & Other
Revenue:
Premium	0	0
Net investment income	0	0
Other income	50	164
Total revenue	50	164
Expenses:
Policy obligations	0	0
Required interest on reserves	0	0
Amortization of acquisition costs	0	0
Commissions, premium taxes, and non-deferred acquisition costs	0	0
Insurance administrative expense	73,907	72,565
Parent expense	2,585	2,640
Stock-based compensation expense	7,679	9,035
Interest expense	24,867	19,944
Total benefits and expenses	109,038	104,184
Subtotal	(108,988)	(104,020)
Non-operating items	0	0
Measure of segment profitability (pretax)	(108,988)	(104,020)
Adjustments
Revenue:
Premium	0	0
Net investment income	0	0
Other income	0	0
Total revenue	0	0
Expenses:
Policy obligations	0	0
Required interest on reserves	0	0
Amortization of acquisition costs	0	0
Commissions, premium taxes, and non-deferred acquisition costs	0	0
Insurance administrative expense		112
Parent expense	0
Stock-based compensation expense	0	0
Interest expense	0	0
Total benefits and expenses	0	112
Subtotal	0	(112)
Non-operating items		112
Measure of segment profitability (pretax)	$ 0	$ 0