Supplementary Data on Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 297,860	$ 293,304	$ 316,821
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	37,210	21,195	16,813
Deferred income tax (benefit) expense	(1,854)	(5,162)	3,349
Lease amortization expense	11,887	13,108	13,959
Realized (gains) and impairment (recoveries) losses on investments	(2,307)	(3,114)	(5,908)
(Gain) loss on disposal of fixed assets	(13)	(15)	75
Net investment (income) loss	(25,944)	5,878	543
(Decrease) increase in deferred compensation	(5,006)	7,611	(1,541)
Decrease (increase) in receivables from affiliates	15,514	(26,548)	(19,505)
Increase in accrued investment income	(157)	(713)	(170)
Decrease in prepaid pension	52,755	41,227	28,798
Decrease (increase) in prepaid expenses and other assets	12,161	(4,771)	(1,707)
Decrease in accounts payable and accrued expenses	(4,823)	(14,307)	(3,627)
Increase (decrease) in commissions payable	8,408	(625)	21,390
Increase (decrease) in accrued agent bonuses	10,279	14,105	(7,409)
(Decrease) increase in contract liability	(3,176)	1,422	2,646
Net cash provided by operating activities	$ 402,794	$ 342,595	$ 364,527