LEASE COST (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lease Cost Table Line Items
Total lease cost	$ 15,609	$ 14,086	$ 45,767	$ 45,118
Depreciation and Amortization
Lease Cost Table Line Items
Amortization of ROU assets - finance leases	1,933	1,855	5,777	5,260
Interest Expense
Lease Cost Table Line Items
Interest on lease liabilities - finance leases	49	43	157	83
Cost of Services
Lease Cost Table Line Items
Operating lease cost (cost resulting from lease payments)	11,446	10,910	35,126	34,256
Short-term Lease, Cost	1,029	1,107	2,909	3,419
Variable Lease, Cost	(1)		(285)
Selling General And Administrative Expenses
Lease Cost Table Line Items
Operating lease cost (cost resulting from lease payments)	530	551	1,493	3,181
Sublease Income	(220)	(126)	(614)	(319)
Restructuring
Lease Cost Table Line Items
Operating lease cost (cost resulting from lease payments)	261		697
Impairment
Lease Cost Table Line Items
Operating lease cost (cost resulting from lease payments)	948		1,456
Other income (expense), net
Lease Cost Table Line Items
Operating lease cost (cost resulting from lease payments)	310	242	839	726
Sublease Income	$ (676)	$ (496)	$ (1,788)	$ (1,488)