MERCHANDISE TRUSTS - Cost and Market Value Associated with Assets Held in Merchandise Trusts (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
West Virginia Trust Receivable
Schedule Of Available For Sale Securities [Line Items]
Fair Value	$ 9,300	$ 8,700
Variable Interest Entity, Primary Beneficiary | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	504,651	497,282
Gross Unrealized Gains	17,205	2,118
Gross Unrealized Losses	(2,474)	(11,152)
Fair Value	519,382	488,248
Variable Interest Entity, Primary Beneficiary | Short-term investments | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	16,211	16,903
Fair Value	16,211	16,903
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	1,392	1,703
Gross Unrealized Gains	23	29
Gross Unrealized Losses	(286)	(475)
Fair Value	1,129	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	525	392
Gross Unrealized Gains	7
Gross Unrealized Losses	(132)	(147)
Fair Value	400	245
Variable Interest Entity, Primary Beneficiary | Fixed maturities | Merchandise Trusts | Corporate debt securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	867	1,311
Gross Unrealized Gains	16	29
Gross Unrealized Losses	(154)	(328)
Fair Value	729	1,012
Variable Interest Entity, Primary Beneficiary | Mutual funds - debt securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	179,111	187,840
Gross Unrealized Gains	6,508	262
Gross Unrealized Losses	(17)	(2,645)
Fair Value	185,602	185,457
Variable Interest Entity, Primary Beneficiary | Mutual funds - equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	47,149	45,023
Gross Unrealized Gains	6,448	110
Gross Unrealized Losses		(18)
Fair Value	53,597	45,115
Variable Interest Entity, Primary Beneficiary | Other investment funds | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	229,256	210,655
Gross Unrealized Gains	2,326	388
Gross Unrealized Losses	(2,083)	(7,784)
Fair Value	229,499	203,259
Variable Interest Entity, Primary Beneficiary | Equity securities | Merchandise Trusts | Level 1
Schedule Of Available For Sale Securities [Line Items]
Cost	13,708	18,097
Gross Unrealized Gains	1,900	1,327
Gross Unrealized Losses	(88)	(213)
Fair Value	15,520	19,211
Variable Interest Entity, Primary Beneficiary | Other invested assets | Merchandise Trusts | Level 2
Schedule Of Available For Sale Securities [Line Items]
Cost	8,502	8,398
Gross Unrealized Gains		2
Gross Unrealized Losses		(17)
Fair Value	8,502	8,383
Variable Interest Entity, Primary Beneficiary | Total investments | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	495,329	488,619
Gross Unrealized Gains	17,205	2,118
Gross Unrealized Losses	(2,474)	(11,152)
Fair Value	510,060	479,585
Variable Interest Entity, Primary Beneficiary | West Virginia Trust Receivable | Merchandise Trusts
Schedule Of Available For Sale Securities [Line Items]
Cost	9,322	8,663
Fair Value	$ 9,322	$ 8,663