Supplementary Data on Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net income	$ 600,314	$ 446,061	$ 298,569
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	56,530	47,415	46,166
Deferred income tax expense (benefit)	4,026	(1,002)	9,468
Lease amortization expense	7,377	6,177	5,554
Losses (gains) and impairment losses on investments	895	15,604	27,953
Loss on disposal of fixed assets	3,874	1,607	172
Net investment (income) loss	(874)	13,772	12,916
Increase (decrease) in deferred compensation	2,677	6,143	(1,463)
Increase in receivables from affiliates	(81,722)	(100,401)	(45,814)
Increase in accrued investment income	(1,611)	(1,157)	(1,998)
Increase in pension asset	(34,516)	(101,250)	0
Increase in pension liability	0	0	15,647
(Increase) decrease in prepaid expenses and other assets	(2,996)	7,729	(25,843)
(Decrease) increase in accounts payable and accrued expenses	(7,517)	7,237	18,993
Increase in commissions payable	54,600	53,681	29,282
Increase (decrease) in accrued agent incentive compensation	7,381	(27,089)	(25,271)
Increase in contract liability	2,811	6,678	1,821
Net cash provided by operating activities	$ 611,249	$ 381,205	$ 366,152