MERCHANDISE TRUSTS - Cost and Market Value Associated with Assets Held in Merchandise Trusts (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Fair Value	$ 9,400	$ 9,700
Variable Interest Entity, Primary Beneficiary \| Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	511,890	515,680
Gross Unrealized Gains	34,936	11,346
Gross Unrealized Losses	(50,507)	(3,161)
Fair Value	496,319	523,865
Cost, Assets held for sale	(13,430)	(6,369)
Gross Unrealized Gains, Assets held for sale		(304)
Gross Unrealized Losses,Assets held for sale	1,631
Fair Value, Assets held for sale	(11,799)	(6,673)
Cost, Excluding assets held for sale	498,460	509,311
Gross Unrealized Gains, Excluding assets held for sale	34,936	11,042
Gross Unrealized Losses, Excluding assets held for sale	(48,876)	(3,161)
Fair Value, Excluding assets held for sale	484,520	517,192
Variable Interest Entity, Primary Beneficiary \| Short-term investments \| Merchandise Trusts \| Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	57,130	144,610
Gross Unrealized Gains	7
Fair Value	57,137	144,610
Variable Interest Entity, Primary Beneficiary \| Fixed maturities \| Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	33,839	1,239
Gross Unrealized Gains	4,248	20
Gross Unrealized Losses	(856)	(198)
Fair Value	37,231	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	343	456
Gross Unrealized Gains	16	6
Gross Unrealized Losses	(61)	(65)
Fair Value	298	397
Variable Interest Entity, Primary Beneficiary \| Fixed maturities \| Merchandise Trusts \| Corporate debt securities \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	10,260	783
Gross Unrealized Gains	1,853	14
Gross Unrealized Losses	(129)	(133)
Fair Value	11,984	664
Variable Interest Entity, Primary Beneficiary \| Fixed maturities \| Merchandise Trusts \| Other Debt Securities \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	23,236
Gross Unrealized Gains	2,379
Gross Unrealized Losses	(666)
Fair Value	24,949
Variable Interest Entity, Primary Beneficiary \| Mutual funds - debt securities \| Merchandise Trusts \| Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	22,924	67,801
Gross Unrealized Gains	552	1,857
Gross Unrealized Losses	(591)	(6)
Fair Value	22,885	69,652
Variable Interest Entity, Primary Beneficiary \| Mutual funds - equity securities \| Merchandise Trusts \| Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	45,861	46,609
Gross Unrealized Gains	2,571	1,744
Gross Unrealized Losses	(21,478)
Fair Value	26,954	48,353
Variable Interest Entity, Primary Beneficiary \| Other investment funds \| Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	292,266	213,024
Gross Unrealized Gains	23,280	6,366
Gross Unrealized Losses	(11,521)	(2,953)
Fair Value	304,025	216,437
Variable Interest Entity, Primary Beneficiary \| Equity securities \| Merchandise Trusts \| Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	45,122	24,386
Gross Unrealized Gains	4,231	1,327
Gross Unrealized Losses	(15,750)	(4)
Fair Value	33,603	25,709
Variable Interest Entity, Primary Beneficiary \| Other invested assets \| Merchandise Trusts \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	5,151	8,360
Gross Unrealized Gains	47	32
Gross Unrealized Losses	(90)
Fair Value	5,108	8,392
Variable Interest Entity, Primary Beneficiary \| Total investments \| Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	502,293	506,029
Gross Unrealized Gains	34,936	11,346
Gross Unrealized Losses	(50,286)	(3,161)
Fair Value	486,943	514,214
Variable Interest Entity, Primary Beneficiary \| West Virginia Trust Receivable \| Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	9,597	9,651
Gross Unrealized Losses	(221)
Fair Value	$ 9,376	$ 9,651

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

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