INDEBTEDNESS (NARRATIVE) (Details) $ in Thousands				12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Feb. 14, 2019	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Initial Borrowing Capacity	$ 900,000			$ 900,000
Maximum borrowing capacity	1,200,000			$ 1,200,000
Credit facility interest rate				1.60%	3.40%
Line of Credit Facility, Interest Rate Description			Base rate loans bear interest at a rate equal to the greatest of (i) Wells Fargo’s prime rate, (ii) one half of 1% in excess of the federal funds effective rate, and (iii) 1.25% in excess of the one month London Interbank Offered Rate (“LIBOR”); plus in each case a margin of 0% to 0.75% based on the Company’s net leverage ratio. Eurodollar loans bear interest at LIBOR plus a margin of 1.0% to 1.75% based on the Company’s net leverage ratio. Alternate currency loans bear interest at rates applicable to their respective currencies.
Description of line of credit agreement			On February 14, 2019, the Company entered into a Fourth Amendment to its Amended and Restated Credit Agreement and Amended and Restated Security Agreement originally dated as of June 3, 2013 (collectively the “Credit Agreement”) for a senior secured revolving credit facility with a syndicate of lenders led by Wells Fargo Bank, National Association, as agent, swing line and fronting lender which matures on February 14, 2024 (the “Credit Facility”).
Line of Credit Facility, Collateral				Letter of credit fees are one eighth of 1% of the stated amount of the letter of credit on the date of issuance, renewal or amendment, plus an annual fee equal to the borrowing margin for Eurodollar loans.
Borrowings outstanding on credit facility	385,000	$ 290,000		$ 385,000	$ 290,000
Line of credit	385,000	290,000		385,000	$ 290,000
Average daily utilization under credit facility	550,900	$ 331,800
Remaining borrowing capacity under credit facility	$ 510,000			$ 510,000
Fed Funds Effective Rate Overnight Index Swap Rate [Member]
Credit facility interest rate				1.00%
London Interbank Offered Rate (LIBOR) [Member]
Credit facility interest rate				1.25%
Minimum
Ratio of Indebtedness to Net Capital	3.50			3.50
Minimum | Company's net leverage ratio [Member]
Credit facility interest rate				0.00%
Minimum | Eurodollar [Member]
Credit facility interest rate				1.00%
Maximum
Ratio of Indebtedness to Net Capital	1.00			1.00
Proceeds from factored receivables	$ 75,000			$ 75,000
Maximum | Company's net leverage ratio [Member]
Credit facility interest rate				0.75%
Maximum | Eurodollar [Member]
Credit facility interest rate				1.75%