DEBT (Details) $ in Thousands, € in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2020 EUR (€)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 EUR (€)
Components of the company's debt obligations
Consolidated Leverage Ratio		1.98	1.98
Consolidated Interest Coverage Ratio		15.50	15.50
Long-term obligations gross including current maturities		$ 1,150,942		$ 1,153,682
Current maturities of long-term obligations		(66,248)		(65,988)
Total long-term obligations		1,084,694		1,087,694
Deferred Finance Costs, Net, Total		1,952		2,241
Deferred debt issuance costs noncurrent		1,952		2,241
Long-term obligations including current maturities		1,148,990		1,151,441
Current maturities of long-term obligations		(66,248)		(65,988)
Long-term obligations, net of unamortized debt issuance costs		1,082,742		1,085,453
Aggregate long-term maturities, excluding finance lease obligations
Year One		62,259
Year Two		59,990
Year Three		133,859
Year Four		338,967
Year Five		274,900
After Year Five		$ 250,404
Minimum
Components of the company's debt obligations
Consolidated Interest Coverage Ratio		3.00	3.00
Maximum
Components of the company's debt obligations
Consolidated Leverage Ratio		3.50	3.50
5-year revolving credit facility maturing in July 2022
Components of the company's debt obligations
Revolving credit facility maximum borrowing capacity		$ 300,000	€ 150.0
Compensating balance requirement		0
Amount outstanding under line of credit		150,000	€ 0.0	25,000	€ 0.0
Notes payable
Components of the company's debt obligations
Proceeds from debt	$ 280,000
Long-term obligations gross including current maturities		168,000		168,000
Deferred Finance Costs, Net, Total		315		390
Long-term obligations including current maturities		$ 167,685		$ 167,610
Interest rate on notes (as a percent)	1.36%	1.36%	1.36%	1.36%	1.36%
Floating interest rate prior to conversion to a fixed interest rate		2.40%	2.40%	3.20%	3.20%
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		$ 15,358		$ 19,220
Long-term obligations including current maturities		$ 15,358		$ 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%	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%	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		52		64
Long-term obligations including current maturities		$ 74,948		$ 74,936
Interest rate on notes (as a percent)		3.20%	3.20%	3.20%	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		126		144
Long-term obligations including current maturities		$ 124,874		$ 124,856
Interest rate on notes (as a percent)		3.50%	3.50%	3.50%	3.50%
Senior unsecured notes 0.98%, due in 2023
Components of the company's debt obligations
Long-term obligations gross including current maturities		$ 112,340		$ 112,170
Deferred Finance Costs, Net, Total		326		356
Long-term obligations including current maturities		$ 112,014		$ 111,814
Interest rate on notes (as a percent)		1.00%	1.00%	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		56		63
Long-term obligations including current maturities		$ 49,944		$ 49,937
Interest rate on notes (as a percent)		3.40%	3.40%	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		126		144
Long-term obligations including current maturities		$ 99,874		$ 99,856
Interest rate on notes (as a percent)		3.50%	3.50%	3.50%	3.50%
Senior unsecured notes 1.17%, due in 2024
Components of the company's debt obligations
Long-term obligations gross including current maturities		$ 224,680		$ 224,340
Deferred Finance Costs, Net, Total		661		742
Long-term obligations including current maturities		$ 224,019		$ 223,598
Interest rate on notes (as a percent)		1.20%	1.20%	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		145		169
Long-term obligations including current maturities		$ 124,855		$ 124,831
Interest rate on notes (as a percent)		3.60%	3.60%	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		145		169
Long-term obligations including current maturities		$ 124,855		$ 124,831
Interest rate on notes (as a percent)		3.60%	3.60%	3.60%	3.60%
Financial lease liabilities
Components of the company's debt obligations
Long-term obligations gross including current maturities		$ 30,564		$ 29,952
Long-term obligations including current maturities		$ 30,564		$ 29,952