Supplementary Data on Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income	$ 446,061	$ 298,569	$ 297,860
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	47,415	46,166	37,210
Deferred income tax (benefit) expense	(1,002)	9,468	(1,854)
Lease amortization expense	6,177	5,554	11,887
Losses (gains) and impairment losses (recoveries) on investments	15,604	27,953	(2,307)
Loss (gain) on disposal of fixed assets	1,607	172	(13)
Net investment loss (income)	13,772	12,916	(25,944)
Increase (decrease) in deferred compensation	6,143	(1,463)	(5,006)
(Increase) decrease in receivables from affiliates	(100,401)	(45,814)	15,514
Increase in accrued investment income	(1,157)	(1,998)	(157)
Increase in pension asset	(101,250)	0	0
Increase in pension liability	0	15,647	52,755
Decrease (increase) in prepaid expenses and other assets	7,729	(25,843)	12,161
Increase (decrease) in accounts payable and accrued expenses	7,237	18,993	(4,823)
Increase in commissions payable	53,681	29,282	8,408
(Decrease) increase in accrued agent incentive compensation	(27,089)	(25,271)	10,279
Increase (decrease) in contract liability	6,678	1,821	(3,176)
Net cash provided by operating activities	$ 381,205	$ 366,152	$ 402,794