MERCHANDISE TRUSTS - Cost and Market Value Associated with Assets Held in Merchandise Trusts (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Fair Value	$ 10,400	$ 10,000
Variable Interest Entity, Primary Beneficiary | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	483,614	486,161
Gross Unrealized Gains	66,099	40,661
Gross Unrealized Losses	(5,445)	(10,538)
Fair Value	544,268	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	61,256	41,039
Gross Unrealized Gains		12
Fair Value	61,256	41,051
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	2,710	25,984
Gross Unrealized Gains	897	2,216
Gross Unrealized Losses		(1,332)
Fair Value	3,607	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	2,709	2,818
Gross Unrealized Gains	897	638
Fair Value	3,606	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	6,097	6,097
Gross Unrealized Gains	206	306
Fair Value	6,303	6,403
Variable Interest Entity, Primary Beneficiary | Mutual funds - equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	26,245	26,356
Gross Unrealized Gains	10,742	43
Gross Unrealized Losses		(154)
Fair Value	36,987	26,245
Variable Interest Entity, Primary Beneficiary | Other investment funds | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	347,273	337,565
Gross Unrealized Gains	44,687	32,461
Gross Unrealized Losses	(4,333)	(8,812)
Fair Value	387,627	361,214
Variable Interest Entity, Primary Beneficiary | Equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	25,725	35,055
Gross Unrealized Gains	9,468	5,544
Gross Unrealized Losses	(968)	(19)
Fair Value	34,225	40,580
Variable Interest Entity, Primary Beneficiary | Other invested assets | Merchandise Trusts | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	3,777	3,875
Gross Unrealized Gains	99	79
Fair Value	3,876	3,954
Variable Interest Entity, Primary Beneficiary | Total investments | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	473,083	475,971
Gross Unrealized Gains	66,099	40,661
Gross Unrealized Losses	(5,301)	(10,317)
Fair Value	533,881	506,315
Variable Interest Entity, Primary Beneficiary | West Virginia Trust Receivable | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	10,531	10,190
Gross Unrealized Losses	(144)	(221)
Fair Value	$ 10,387	$ 9,969