MERCHANDISE TRUSTS - Cost and Market Value Associated with Assets Held in Merchandise Trusts (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Fair Value	$ 10,300	$ 10,000
Variable Interest Entity, Primary Beneficiary | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	515,022	486,161
Gross Unrealized Gains	40,161	40,661
Gross Unrealized Losses	(6,642)	(10,538)
Fair Value	548,541	516,284
Fair Value, Assets held for sale		(14,831)
Fair Value, Excluding assets held for sale		501,453
Variable Interest Entity, Primary Beneficiary | Short-term investments | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	40,665	41,039
Gross Unrealized Gains		12
Fair Value	40,665	41,051
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	2,712	25,984
Gross Unrealized Gains	890	2,216
Gross Unrealized Losses		(1,332)
Fair Value	3,602	26,868
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | U.S. governmental securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	1	1
Fair Value	1	1
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | Corporate debt securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	2,711	2,818
Gross Unrealized Gains	890	638
Fair Value	3,601	3,456
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | Other Debt Securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost		23,165
Gross Unrealized Gains		1,578
Gross Unrealized Losses		(1,332)
Fair Value		23,411
Variable Interest Entity, Primary Beneficiary | Mutual funds - debt securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	6,096	6,097
Gross Unrealized Gains	148	306
Fair Value	6,244	6,403
Variable Interest Entity, Primary Beneficiary | Mutual funds - equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	1,021	26,356
Gross Unrealized Gains	293	43
Gross Unrealized Losses		(154)
Fair Value	1,314	26,245
Variable Interest Entity, Primary Beneficiary | Other investment funds | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	427,072	337,565
Gross Unrealized Gains	33,902	32,461
Gross Unrealized Losses	(4,752)	(8,812)
Fair Value	456,222	361,214
Variable Interest Entity, Primary Beneficiary | Equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	23,155	35,055
Gross Unrealized Gains	4,840	5,544
Gross Unrealized Losses	(1,587)	(19)
Fair Value	26,408	40,580
Variable Interest Entity, Primary Beneficiary | Other invested assets | Merchandise Trusts | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	3,733	3,875
Gross Unrealized Gains	88	79
Fair Value	3,821	3,954
Variable Interest Entity, Primary Beneficiary | Total investments | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	504,454	475,971
Gross Unrealized Gains	40,161	40,661
Gross Unrealized Losses	(6,339)	(10,317)
Fair Value	538,276	506,315
Variable Interest Entity, Primary Beneficiary | West Virginia Trust Receivable | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	10,568	10,190
Gross Unrealized Losses	(303)	(221)
Fair Value	$ 10,265	$ 9,969