DEBT (Details) € in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 EUR (€)	Sep. 30, 2018 USD ($)	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				$ 35,000	$ 0
Consolidated Leverage Ratio			2.05	2.05
Consolidated Interest Coverage Ratio			12.36	12.36
Long-term obligations gross including current maturities				$ 1,198,738	1,256,375
Current maturities of long-term obligations				(64,039)	(61,833)
Total long-term obligations				1,134,699	1,194,542
Deferred Finance Costs, Net, Total				2,962	3,396
Deferred debt issuance costs noncurrent				2,962	3,396
Long-term obligations including current maturities				1,195,776	1,252,979
Current maturities of long-term obligations				(64,039)	(61,833)
Long-term obligations, net of unamortized debt issuance costs				1,131,737	1,191,146
Aggregate long-term maturities, excluding capital lease obligations
2018				62,477
2019				60,379
2020				58,316
2021				133,284
2022				117,219
Thereafter				$ 758,131
Minimum
Long-Term Obligations
Consolidated Interest Coverage Ratio			3.00	3.00
Maximum
Long-Term Obligations
Consolidated Leverage Ratio			3.50	3.50
Revolving credit facility
Long-Term Obligations
Amount outstanding under line of credit | €			€ 89,500
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				$ 224,000	280,000
Deferred Finance Costs, Net, Total				578	692
Long-term obligations including current maturities				$ 223,422	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%	3.60%	3.60%
Notes payable 0.00% - 18.00%, due in monthly and annual installments through 2025
Long-Term Obligations
Long-term obligations gross including current maturities				$ 17,521	15,349
Long-term obligations including current maturities				$ 17,521	$ 15,349
Notes payable 0.00% - 18.00%, due in monthly and annual installments through 2025 | Minimum
Long-Term Obligations
Interest rate on notes (as a percent)			0.00%	0.00%	0.61%
Notes payable 0.00% - 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%	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				94	113
Long-term obligations including current maturities				$ 74,906	$ 74,887
Interest rate on notes (as a percent)			3.20%	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				190	217
Long-term obligations including current maturities				$ 124,810	$ 124,783
Interest rate on notes (as a percent)			3.50%	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				$ 116,095	$ 120,095
Deferred Finance Costs, Net, Total				456	526
Long-term obligations including current maturities				115,639	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				80	89
Long-term obligations including current maturities				$ 49,920	$ 49,911
Interest rate on notes (as a percent)			3.40%	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				190	217
Long-term obligations including current maturities				$ 99,810	$ 99,783
Interest rate on notes (as a percent)			3.50%	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				$ 232,190	$ 240,190
Deferred Finance Costs, Net, Total				944	1,066
Long-term obligations including current maturities				231,246	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				215	238
Long-term obligations including current maturities				$ 124,785	$ 124,762
Interest rate on notes (as a percent)			3.60%	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				215	238
Long-term obligations including current maturities				$ 124,785	$ 124,762
Interest rate on notes (as a percent)			3.60%	3.60%	3.60%
Capital lease obligations
Long-Term Obligations
Long-term obligations gross including current maturities				$ 8,932	$ 741
Long-term obligations including current maturities				$ 8,932	$ 741