MERCHANDISE TRUSTS - Cost and Market Value Associated with Assets Held in Merchandise Trusts (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Fair Value	$ 9,300	$ 9,700
Variable Interest Entity, Primary Beneficiary | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	501,015	515,680
Gross Unrealized Gains	27,413	11,346
Gross Unrealized Losses	(44,120)	(3,161)
Fair Value	484,308	523,865
Cost, Assets held for sale	(12,154)	(6,369)
Gross Unrealized Gains, Assets held for sale		(304)
Gross Unrealized Losses,Assets held for sale	346
Fair Value, Assets held for sale	(11,808)	(6,673)
Cost, Excluding assets held for sale	488,861	509,311
Gross Unrealized Gains, Excluding assets held for sale	27,413	11,042
Gross Unrealized Losses, Excluding assets held for sale	(43,774)	(3,161)
Fair Value, Excluding assets held for sale	472,500	517,192
Variable Interest Entity, Primary Beneficiary | Short-term investments | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	104,706	144,610
Fair Value	104,706	144,610
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	37,413	1,239
Gross Unrealized Gains	3,190	20
Gross Unrealized Losses	(207)	(198)
Fair Value	40,396	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	355	456
Gross Unrealized Gains	18	6
Gross Unrealized Losses	(72)	(65)
Fair Value	301	397
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | Corporate debt securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	13,472	783
Gross Unrealized Gains	1,346	14
Gross Unrealized Losses	(126)	(133)
Fair Value	14,692	664
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | Other Debt Securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	23,586
Gross Unrealized Gains	1,826
Gross Unrealized Losses	(9)
Fair Value	25,403
Variable Interest Entity, Primary Beneficiary | Mutual funds - debt securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	22,786	67,801
Gross Unrealized Gains	458	1,857
Gross Unrealized Losses	(820)	(6)
Fair Value	22,424	69,652
Variable Interest Entity, Primary Beneficiary | Mutual funds - equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	46,039	46,609
Gross Unrealized Gains	2,367	1,744
Gross Unrealized Losses	(17,283)
Fair Value	31,123	48,353
Variable Interest Entity, Primary Beneficiary | Other investment funds | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	230,105	213,024
Gross Unrealized Gains	19,853	6,366
Gross Unrealized Losses	(13,618)	(2,953)
Fair Value	236,340	216,437
Variable Interest Entity, Primary Beneficiary | Equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	45,097	24,386
Gross Unrealized Gains	1,519	1,327
Gross Unrealized Losses	(11,971)	(4)
Fair Value	34,645	25,709
Variable Interest Entity, Primary Beneficiary | Other invested assets | Merchandise Trusts | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	5,355	8,360
Gross Unrealized Gains	26	32
Fair Value	5,381	8,392
Variable Interest Entity, Primary Beneficiary | Total investments | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	491,501	506,029
Gross Unrealized Gains	27,413	11,346
Gross Unrealized Losses	(43,899)	(3,161)
Fair Value	475,015	514,214
Variable Interest Entity, Primary Beneficiary | West Virginia Trust Receivable | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	9,514	9,651
Gross Unrealized Losses	(221)
Fair Value	$ 9,293	$ 9,651