MERCHANDISE TRUSTS - Cost and Market Value Associated with Assets Held in Merchandise Trusts (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Fair Value	$ 9,700	$ 8,700
Variable Interest Entity, Primary Beneficiary | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	515,680	497,282
Gross Unrealized Gains	11,346	2,118
Gross Unrealized Losses	(3,161)	(11,152)
Fair Value	523,865	488,248
Cost, Assets held for sale	(6,369)
Gross Unrealized Gains, Assets held for sale	(304)
Fair Value, Assets held for sale	(6,673)
Cost, Excluding assets held for sale	509,311
Gross Unrealized Gains, Excluding assets held for sale	11,042
Gross Unrealized Losses, Excluding assets held for sale	(3,161)
Fair Value, Excluding assets held for sale	517,192
Variable Interest Entity, Primary Beneficiary | Short-term investments | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	144,610	16,903
Fair Value	144,610	16,903
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	1,239	1,703
Gross Unrealized Gains	20	29
Gross Unrealized Losses	(198)	(475)
Fair Value	1,061	1,257
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | U.S. governmental securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	456	392
Gross Unrealized Gains	6
Gross Unrealized Losses	(65)	(147)
Fair Value	397	245
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | Corporate debt securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	783	1,311
Gross Unrealized Gains	14	29
Gross Unrealized Losses	(133)	(328)
Fair Value	664	1,012
Variable Interest Entity, Primary Beneficiary | Mutual funds - debt securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	67,801	187,840
Gross Unrealized Gains	1,857	262
Gross Unrealized Losses	(6)	(2,645)
Fair Value	69,652	185,457
Variable Interest Entity, Primary Beneficiary | Mutual funds - equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	46,609	45,023
Gross Unrealized Gains	1,744	110
Gross Unrealized Losses		(18)
Fair Value	48,353	45,115
Variable Interest Entity, Primary Beneficiary | Other investment funds | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	213,024	210,655
Gross Unrealized Gains	6,366	388
Gross Unrealized Losses	(2,953)	(7,784)
Fair Value	216,437	203,259
Variable Interest Entity, Primary Beneficiary | Equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	24,386	18,097
Gross Unrealized Gains	1,327	1,327
Gross Unrealized Losses	(4)	(213)
Fair Value	25,709	19,211
Variable Interest Entity, Primary Beneficiary | Other invested assets | Merchandise Trusts | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	8,360	8,398
Gross Unrealized Gains	32	2
Gross Unrealized Losses		(17)
Fair Value	8,392	8,383
Variable Interest Entity, Primary Beneficiary | Total investments | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	506,029	488,619
Gross Unrealized Gains	11,346	2,118
Gross Unrealized Losses	(3,161)	(11,152)
Fair Value	514,214	479,585
Variable Interest Entity, Primary Beneficiary | West Virginia Trust Receivable | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	9,651	8,663
Fair Value	$ 9,651	$ 8,663