LONG-TERM OBLIGATIONS (Details) € in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Long-Term Obligations
Revolving credit facility maximum borrowing capacity	$ 300,000
Revolving credit facility maturity date	Jul. 01, 2022
Amount outstanding under line of credit	$ 0			$ 0
Consolidated Leverage Ratio	1.15
Consolidated Interest Coverage Ratio	12.12
Long-term obligations gross including current maturities	$ 1,264,731			1,256,375
Current maturities of long-term obligations	(61,505)			(61,833)
Total long-term obligations	1,203,226			1,194,542
Deferred Finance Costs, Net, Total	3,251			3,396
Deferred debt issuance costs noncurrent	3,251			3,396
Long-term obligations including current maturities	1,261,480			1,252,979
Current maturities of long-term obligations	(61,505)			(61,833)
Long-term obligations, net of unamortized debt issuance costs	1,199,975			1,191,146
Aggregate long-term maturities, excluding capital lease obligations
2018	61,047
2019	59,105
2020	57,991
2021	57,993
2022	132,823
Thereafter	$ 895,218
Minimum
Long-Term Obligations
Consolidated Interest Coverage Ratio	3.00
Maximum
Long-Term Obligations
Consolidated Leverage Ratio	3.50
Revolving credit facility
Long-Term Obligations
Proceeds from debt | €		€ 150,000
Term of debt		5 years	5 years
Interest rate on notes (as a percent)		1.10%	1.10%
Notes payable to banks
Long-Term Obligations
Proceeds from debt			$ 280,000
Term of debt		5 years	5 years
Long-term obligations gross including current maturities	$ 280,000			280,000
Deferred Finance Costs, Net, Total	654			692
Long-term obligations including current maturities	279,346			279,308
Interest rate on notes (as a percent)		1.36%	1.36%
Floating interest rate prior to conversion to a fixed interest rate		2.56%	2.56%
Notes payable 0.61% - 18.00%, due in monthly and annual installments through 2025
Long-Term Obligations
Long-term obligations gross including current maturities	14,607			15,349
Long-term obligations including current maturities	$ 14,607			$ 15,349
Notes payable 0.61% - 18.00%, due in monthly and annual installments through 2025 | Minimum
Long-Term Obligations
Interest rate on notes (as a percent)	0.61%			0.61%
Notes payable 0.61% - 18.00%, due in monthly and annual installments through 2025 | Maximum
Long-Term Obligations
Interest rate on notes (as a percent)	18.00%			18.00%
Senior unsecured notes 3.2%, due in 2022
Long-Term Obligations
Long-term obligations gross including current maturities	$ 75,000			$ 75,000
Deferred Finance Costs, Net, Total	107			113
Long-term obligations including current maturities	$ 74,893			$ 74,887
Interest rate on notes (as a percent)	3.20%			3.20%
Senior unsecured notes 3.5%, due in 2023
Long-Term Obligations
Long-term obligations gross including current maturities	$ 125,000			$ 125,000
Deferred Finance Costs, Net, Total	208			217
Long-term obligations including current maturities	$ 124,792			$ 124,783
Interest rate on notes (as a percent)	3.50%			3.50%
Senior unsecured notes 0.98%, due in 2023
Long-Term Obligations
Proceeds from private placement | €		€ 100,000
Term of debt		6 years	6 years
Long-term obligations gross including current maturities	$ 123,190			$ 120,095
Deferred Finance Costs, Net, Total	503			526
Long-term obligations including current maturities	122,687			119,569
Interest rate on notes (as a percent)		0.98%	0.98%
Senior unsecured notes 3.4%, due in 2024
Long-Term Obligations
Long-term obligations gross including current maturities	50,000			50,000
Deferred Finance Costs, Net, Total	86			89
Long-term obligations including current maturities	$ 49,914			$ 49,911
Interest rate on notes (as a percent)	3.40%			3.40%
Senior unsecured notes 3.5%, due in 2024
Long-Term Obligations
Long-term obligations gross including current maturities	$ 100,000			$ 100,000
Deferred Finance Costs, Net, Total	208			217
Long-term obligations including current maturities	$ 99,792			$ 99,783
Interest rate on notes (as a percent)	3.50%			3.50%
Senior unsecured notes 1.17%, due in 2024
Long-Term Obligations
Proceeds from private placement | €		€ 200,000
Term of debt		7 years	7 years
Long-term obligations gross including current maturities	$ 246,380			$ 240,190
Deferred Finance Costs, Net, Total	1,025			1,066
Long-term obligations including current maturities	245,355			239,124
Interest rate on notes (as a percent)		1.17%	1.17%
Senior unsecured notes 3.6%, due in 2025
Long-Term Obligations
Long-term obligations gross including current maturities	125,000			125,000
Deferred Finance Costs, Net, Total	230			238
Long-term obligations including current maturities	$ 124,770			$ 124,762
Interest rate on notes (as a percent)	3.60%			3.60%
Senior unsecured notes 3.6%, due in 2026
Long-Term Obligations
Long-term obligations gross including current maturities	$ 125,000			$ 125,000
Deferred Finance Costs, Net, Total	230			238
Long-term obligations including current maturities	$ 124,770			$ 124,762
Interest rate on notes (as a percent)	3.60%			3.60%
Capital lease obligations
Long-Term Obligations
Long-term obligations gross including current maturities	$ 554			$ 741
Long-term obligations including current maturities	$ 554			$ 741