Supplementary Data on Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities:
Net income	$ 559,335	$ 600,314	$ 446,061
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	69,450	56,530	47,415
Deferred income tax expense (benefit)	19,547	4,026	(1,002)
Lease amortization expense	7,333	7,377	6,177
Losses and impairments on investments	976	895	15,604
Loss on disposal and impairments of fixed assets	(5,741)	(3,874)	(1,607)
Net investment (income) loss	(4,385)	(874)	13,772
Receipt of donated equipment and other	(2,634)	0	0
(Decrease) increase in deferred compensation	(3,119)	2,677	6,143
Increase in receivables from affiliates	(28,529)	(81,722)	(100,401)
Increase in accrued investment income	(3,242)	(1,611)	(1,157)
Increase in pension asset	(29,380)	(34,516)	(101,250)
Decrease (increase) in prepaid expenses and other assets	22,345	(2,996)	7,729
(Decrease) increase in accounts payable and accrued expenses	(7,798)	(7,517)	7,237
Increase in commissions payable	17,011	54,600	53,681
Increase (decrease) in accrued agent incentive compensation	57,102	7,381	(27,089)
Increase in contract liability	6,904	2,811	6,678
Net cash provided by operating activities	$ 686,657	$ 611,249	$ 381,205