MERCHANDISE TRUSTS - Cost and Market Value Associated with Assets Held in Merchandise Trusts (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Fair Value	$ 10,100	$ 10,000
Variable Interest Entity, Primary Beneficiary | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	493,457	486,161
Gross Unrealized Gains	53,850	40,661
Gross Unrealized Losses	(7,273)	(10,538)
Fair Value	540,034	516,284
Fair Value, Assets held for sale	(15,411)	(14,831)
Fair Value, Excluding assets held for sale	524,623	501,453
Variable Interest Entity, Primary Beneficiary | Short-term investments | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	78,231	41,039
Gross Unrealized Gains	12	12
Fair Value	78,243	41,051
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	26,587	25,984
Gross Unrealized Gains	4,092	2,216
Gross Unrealized Losses	(2)	(1,332)
Fair Value	30,677	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	2,883	2,818
Gross Unrealized Gains	695	638
Gross Unrealized Losses	(2)
Fair Value	3,576	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	23,703	23,165
Gross Unrealized Gains	3,397	1,578
Gross Unrealized Losses		(1,332)
Fair Value	27,100	23,411
Variable Interest Entity, Primary Beneficiary | Mutual funds - debt securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	6,097	6,097
Gross Unrealized Gains	134	306
Gross Unrealized Losses	(2)
Fair Value	6,229	6,403
Variable Interest Entity, Primary Beneficiary | Mutual funds - equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	26,237	26,356
Gross Unrealized Gains	5,066	43
Gross Unrealized Losses		(154)
Fair Value	31,303	26,245
Variable Interest Entity, Primary Beneficiary | Other investment funds | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	303,414	337,565
Gross Unrealized Gains	32,832	32,461
Gross Unrealized Losses	(5,749)	(8,812)
Fair Value	330,497	361,214
Variable Interest Entity, Primary Beneficiary | Equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	38,768	35,055
Gross Unrealized Gains	11,630	5,544
Gross Unrealized Losses	(1,299)	(19)
Fair Value	49,099	40,580
Variable Interest Entity, Primary Beneficiary | Other invested assets | Merchandise Trusts | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	3,812	3,875
Gross Unrealized Gains	84	79
Fair Value	3,896	3,954
Variable Interest Entity, Primary Beneficiary | Total investments | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	483,146	475,971
Gross Unrealized Gains	53,850	40,661
Gross Unrealized Losses	(7,052)	(10,317)
Fair Value	529,944	506,315
Variable Interest Entity, Primary Beneficiary | West Virginia Trust Receivable | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	10,311	10,190
Gross Unrealized Losses	(221)	(221)
Fair Value	$ 10,090	$ 9,969