RESTRICTED CASH AND INVESTMENTS (Details) $ in Thousands	Sep. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Restricted Cash and Investments [Line Items]
Cash collateral held by insurance carriers	$ 24,054	$ 22,926
Cash and cash equivalents held in Trust	28,494	16,113
Investments held in Trust	162,519	171,752
Deferred compensation mutual funds	25,410	22,428
Other restricted cash and cash equivalents	157	6,012
Restricted cash and investments	240,634	239,231
Held-to-maturity Securities, Reconciliation to Fair Value [Abstract]
Gross Unrealized Gain	128	1,324
Gross Unrealized Loss	(2,409)	(838)
Fair Value	160,238	172,238
Estimated fair value
Less than 12 months	104,201	73,392
12 months or more	38,424	20,600
Total	142,625	93,992
Unrealized losses
Less than 12 months	(1,259)	(445)
12 months or more	(1,150)	(393)
Total	$ (2,409)	$ (838)
Securities in unrealized loss positions, number of positions \| security	124	83
Held-to-maturity Securities, Investment Maturities, Fair Value [Abstract]
Fair Value	$ 160,238	$ 172,238
Municipal debt securities
Restricted Cash and Investments [Line Items]
Investments held in Trust	77,211	82,770
Held-to-maturity Securities, Reconciliation to Fair Value [Abstract]
Gross Unrealized Gain	124	974
Gross Unrealized Loss	(1,101)	(378)
Fair Value	76,234	83,366
Estimated fair value
Less than 12 months	49,727	23,078
12 months or more	11,531	9,631
Total	61,258	32,709
Unrealized losses
Less than 12 months	(515)	(124)
12 months or more	(586)	(254)
Total	(1,101)	(378)
Held-to-maturity Securities, Investment Maturities, Fair Value [Abstract]
Fair Value	76,234	83,366
Corporate debt securities
Restricted Cash and Investments [Line Items]
Investments held in Trust	81,414	83,916
Held-to-maturity Securities, Reconciliation to Fair Value [Abstract]
Gross Unrealized Gain	1	309
Gross Unrealized Loss	(1,221)	(434)
Fair Value	80,194	83,791
Estimated fair value
Less than 12 months	52,187	48,952
12 months or more	26,020	10,081
Total	78,207	59,033
Unrealized losses
Less than 12 months	(689)	(311)
12 months or more	(532)	(123)
Total	(1,221)	(434)
Held-to-maturity Securities, Investment Maturities, Fair Value [Abstract]
Fair Value	80,194	83,791
Agency mortgage-backed securities
Restricted Cash and Investments [Line Items]
Investments held in Trust	2,895	4,066
Held-to-maturity Securities, Reconciliation to Fair Value [Abstract]
Gross Unrealized Gain	3	22
Gross Unrealized Loss	(52)	(26)
Fair Value	2,846	4,062
Estimated fair value
Less than 12 months	1,323	1,362
12 months or more	873	888
Total	2,196	2,250
Unrealized losses
Less than 12 months	(20)	(10)
12 months or more	(32)	(16)
Total	(52)	(26)
Held-to-maturity Securities, Investment Maturities, Fair Value [Abstract]
Fair Value	2,846	4,062
U.S. government and agency securities
Restricted Cash and Investments [Line Items]
Investments held in Trust	999	1,000
Held-to-maturity Securities, Reconciliation to Fair Value [Abstract]
Gross Unrealized Gain	0	19
Gross Unrealized Loss	(35)	0
Fair Value	964	1,019
Estimated fair value
Less than 12 months	964
12 months or more	0
Total	964
Unrealized losses
Less than 12 months	(35)
12 months or more	0
Total	(35)
Held-to-maturity Securities, Investment Maturities, Fair Value [Abstract]
Fair Value	964	$ 1,019
Restricted Cash and Investments
Restricted Cash and Investments [Line Items]
Investments held in Trust	162,519
Held-to-maturity Securities, Reconciliation to Fair Value [Abstract]
Fair Value	160,238
Held-to-maturity Securities, Investment Maturities, Amortized Cost [Abstract]
Due in one year or less	28,294
Due after one year through five years	87,267
Due after five years through ten years	46,958
Held-to-maturity Securities, Investment Maturities, Fair Value [Abstract]
Due in one year or less	28,133
Due after one year through five years	86,225
Due after five years through ten years	45,880
Fair Value	$ 160,238

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