DEBT (Long-Term Obligations) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2017
Components of the company's debt obligations
Consolidated Leverage Ratio	1.81
Consolidated Interest Coverage Ratio	15.92
Finance Lease, Liability, Noncurrent	$ 30,115	$ 29,952
Long-term Debt and Lease Obligation, Gross	1,107,798	1,153,682
Debt Instrument and Lease Obligations Carrying Amount Current Maturities	(66,056)	(65,988)
Total long-term obligations	1,041,742	1,087,694
Deferred Finance Costs, Net, Total	1,807	2,241
Deferred debt issuance costs noncurrent	1,807	2,241
Long-term obligations including current maturities	1,105,991	1,151,441
Current maturities of long-term obligations	(66,056)	(65,988)
Long-Term Obligations, net of unamortized debt issuance costs	1,039,935	1,085,453
Aggregate long-term maturities, excluding finance lease obligations
Year One	62,023
Year Two	134,772
Year Three	119,655
Year Four	510,581
Year Five	229
After Year Five	$ 250,423
Minimum
Components of the company's debt obligations
Consolidated Interest Coverage Ratio	3.00
Maximum
Components of the company's debt obligations
Consolidated Leverage Ratio	3.50
Notes payable 0.00% – 10.90%, due in monthly and annual installments through 2028
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 13,993	19,220
Deferred Finance Costs, Net, Total	0	0
Long-term debt	$ 13,993	$ 19,220
Notes payable 0.00% – 10.90%, due in monthly and annual installments through 2028 | Minimum
Components of the company's debt obligations
Interest rate on notes (as a percent)	0.00%	0.00%
Notes payable 0.00% – 10.90%, due in monthly and annual installments through 2028 | Maximum
Components of the company's debt obligations
Interest rate on notes (as a percent)	10.90%	10.90%
Senior unsecured notes 3.2%, due in 2022
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 75,000	$ 75,000
Deferred Finance Costs, Net, Total	44	64
Long-term debt	$ 74,956	$ 74,936
Interest rate on notes (as a percent)	3.20%	3.20%
Senior unsecured debts 1.8% USD floating swapped to 1.36% EUR fixed, equal annual installments through 2022
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 112,000	$ 168,000
Deferred Finance Costs, Net, Total	277	390
Long-term debt	$ 111,723	$ 167,610
Interest rate on notes (as a percent)	1.36%	1.36%	1.36%
Floating interest rate prior to conversion to a fixed interest rate	1.80%	3.20%
Senior unsecured notes 3.5%, due in 2023
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 125,000	$ 125,000
Deferred Finance Costs, Net, Total	116	144
Long-term debt	$ 124,884	$ 124,856
Interest rate on notes (as a percent)	3.50%	3.50%
Senior unsecured notes 1.0%, due in 2023
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 117,230	$ 112,170
Deferred Finance Costs, Net, Total	312	356
Long-term debt	$ 116,918	$ 111,814
Interest rate on notes (as a percent)	1.00%	1.00%
Senior unsecured notes 3.4%, due in 2024
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 50,000	$ 50,000
Deferred Finance Costs, Net, Total	53	63
Long-term debt	$ 49,947	$ 49,937
Interest rate on notes (as a percent)	3.40%	3.40%
Senior unsecured notes 3.5%, due in 2024
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 100,000	$ 100,000
Deferred Finance Costs, Net, Total	116	144
Long-term debt	$ 99,884	$ 99,856
Interest rate on notes (as a percent)	3.50%	3.50%
Senior unsecured notes 1.2%, due in 2024
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 234,460	$ 224,340
Deferred Finance Costs, Net, Total	621	742
Long-term debt	$ 233,839	$ 223,598
Interest rate on notes (as a percent)	1.20%	1.20%
Senior unsecured notes 3.6%, due in 2025
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 125,000	$ 125,000
Deferred Finance Costs, Net, Total	134	169
Long-term debt	$ 124,866	$ 124,831
Interest rate on notes (as a percent)	3.60%	3.60%
Senior unsecured notes 3.6%, due in 2026
Components of the company's debt obligations
Long-term obligations gross including current maturities	$ 125,000	$ 125,000
Deferred Finance Costs, Net, Total	134	169
Long-term debt	$ 124,866	$ 124,831
Interest rate on notes (as a percent)	3.60%	3.60%