GOODWILL AND INTANGIBLE ASSETS - Intangible Assets Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Finite lived intangible assets:
Intangible assets, gross	$ 124,248	$ 124,248
Accumulated amortization	(77,554)	(73,343)
Intangible assets, net	46,694	50,905
Customer relationship intangibles
Finite lived intangible assets:
Finite lived intangible assets	113,150	113,150
Other intangibles, primarily trade name
Finite lived intangible assets:
Finite lived intangible assets	2,367	2,367
Trade Names
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Indefinite lived intangible assets — Trade name	8,731	8,731
FMS
Finite lived intangible assets:
Intangible assets, gross	57,686	57,686
Accumulated amortization	(50,655)	(49,031)
Intangible assets, net	7,031	8,655
FMS | Customer relationship intangibles
Finite lived intangible assets:
Finite lived intangible assets	56,050	56,050
FMS | Other intangibles, primarily trade name
Finite lived intangible assets:
Finite lived intangible assets	1,636	1,636
FMS | Trade Names
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Indefinite lived intangible assets — Trade name	0	0
SCS
Finite lived intangible assets:
Intangible assets, gross	50,249	50,249
Accumulated amortization	(22,397)	(20,047)
Intangible assets, net	27,852	30,202
SCS | Customer relationship intangibles
Finite lived intangible assets:
Finite lived intangible assets	49,518	49,518
SCS | Other intangibles, primarily trade name
Finite lived intangible assets:
Finite lived intangible assets	731	731
SCS | Trade Names
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Indefinite lived intangible assets — Trade name	0	0
DTS
Finite lived intangible assets:
Intangible assets, gross	7,582	7,582
Accumulated amortization	(4,502)	(4,265)
Intangible assets, net	3,080	3,317
DTS | Customer relationship intangibles
Finite lived intangible assets:
Finite lived intangible assets	7,582	7,582
DTS | Other intangibles, primarily trade name
Finite lived intangible assets:
Finite lived intangible assets	0	0
DTS | Trade Names
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Indefinite lived intangible assets — Trade name	0	0
CSS
Finite lived intangible assets:
Intangible assets, gross	8,731	8,731
Accumulated amortization	0	0
Intangible assets, net	8,731	8,731
CSS | Customer relationship intangibles
Finite lived intangible assets:
Finite lived intangible assets	0	0
CSS | Other intangibles, primarily trade name
Finite lived intangible assets:
Finite lived intangible assets	0	0
CSS | Trade Names
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Indefinite lived intangible assets — Trade name	$ 8,731	$ 8,731