MERCHANDISE TRUSTS - Cost and Market Value Associated with Assets Held in Merchandise Trusts (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Fair Value	$ 10,000	$ 9,700
Variable Interest Entity, Primary Beneficiary | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	486,161	515,680
Gross Unrealized Gains	40,661	11,346
Gross Unrealized Losses	(10,538)	(3,161)
Fair Value	516,284	523,865
Fair Value, Assets held for sale	(14,831)	(46,700)
Cost, Excluding assets held for sale	486,161	515,680
Gross Unrealized Gains, Excluding assets held for sale	40,661	11,346
Gross Unrealized Losses, Excluding assets held for sale	(10,538)	(3,161)
Fair Value, Excluding assets held for sale	501,453	477,165
Variable Interest Entity, Primary Beneficiary | Short-term investments | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	41,039	144,610
Gross Unrealized Gains	12
Fair Value	41,051	144,610
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	25,984	1,239
Gross Unrealized Gains	2,216	20
Gross Unrealized Losses	(1,332)	(198)
Fair Value	26,868	1,061
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	456
Gross Unrealized Gains		6
Gross Unrealized Losses		(65)
Fair Value	1	397
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | Corporate debt securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	2,818	783
Gross Unrealized Gains	638	14
Gross Unrealized Losses		(133)
Fair Value	3,456	664
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	67,801
Gross Unrealized Gains	306	1,857
Gross Unrealized Losses		(6)
Fair Value	6,403	69,652
Variable Interest Entity, Primary Beneficiary | Mutual funds - equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	26,356	46,609
Gross Unrealized Gains	43	1,744
Gross Unrealized Losses	(154)
Fair Value	26,245	48,353
Variable Interest Entity, Primary Beneficiary | Other investment funds | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	337,565	213,024
Gross Unrealized Gains	32,461	6,366
Gross Unrealized Losses	(8,812)	(2,953)
Fair Value	361,214	216,437
Variable Interest Entity, Primary Beneficiary | Equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	35,055	24,386
Gross Unrealized Gains	5,544	1,327
Gross Unrealized Losses	(19)	(4)
Fair Value	40,580	25,709
Variable Interest Entity, Primary Beneficiary | Other invested assets | Merchandise Trusts | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	3,875	8,360
Gross Unrealized Gains	79	32
Fair Value	3,954	8,392
Variable Interest Entity, Primary Beneficiary | Total investments | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	475,971	506,029
Gross Unrealized Gains	40,661	11,346
Gross Unrealized Losses	(10,317)	(3,161)
Fair Value	506,315	514,214
Variable Interest Entity, Primary Beneficiary | West Virginia Trust Receivable | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	10,190	9,651
Gross Unrealized Losses	(221)
Fair Value	$ 9,969	$ 9,651