SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Balances Related to Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 118,700	$ 124,200
Less accumulated depreciation	(95,024)	(96,137)
Property and equipment, net	23,719	28,113
Building and Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,000	8,700
Equipment and Furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	53,100	55,600
Finance Leases [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,900	5,200
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 50,700	$ 54,700

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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-Name Accounting Standards Codification
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-SubTopic 10
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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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