DEBT (Details) $ in Thousands, € in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Mar. 31, 2019 EUR (€)	Mar. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 USD ($)
Long-Term Obligations
Consolidated Leverage Ratio		2.00	2.00
Consolidated Interest Coverage Ratio		14.75	14.75
Long-term obligations gross including current maturities			$ 1,207,717			$ 1,191,489
Current maturities of long-term obligations			(63,981)			(62,678)
Total long-term obligations			1,143,736			1,128,811
Deferred Finance Costs, Net, Total			2,674			2,818
Deferred debt issuance costs noncurrent			2,674			2,818
Long-term obligations including current maturities			1,205,043			1,188,671
Current maturities of long-term obligations			(63,981)	$ (65,309)		(62,678)
Long-term obligations, net of unamortized debt issuance costs			1,141,062	$ 1,129,238		1,125,993
Aggregate long-term maturities, excluding finance lease obligations
Year One			60,592
Year Two			62,195
Year Three			61,111
Year Four			135,252
Year Five			339,883
After Year Five			$ 524,883
Minimum
Long-Term Obligations
Consolidated Interest Coverage Ratio		3.00	3.00
Maximum
Long-Term Obligations
Consolidated Leverage Ratio		3.50	3.50
5-year revolving credit facility maturing in July 2022
Long-Term Obligations
Revolving credit facility maximum borrowing capacity		€ 150.0	$ 300,000
Amount outstanding under line of credit | €		€ 0.0			€ 69.0
Notes payable to banks
Long-Term Obligations
Proceeds from debt	$ 280,000
Long-term obligations gross including current maturities			224,000			224,000
Deferred Finance Costs, Net, Total			503			541
Long-term obligations including current maturities			$ 223,497			$ 223,459
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		4.30%	4.30%		4.00%	4.00%
Notes payable 0.00% - 16.00%, due in monthly and annual installments through 2028
Long-Term Obligations
Long-term obligations gross including current maturities			$ 23,421			$ 15,531
Long-term obligations including current maturities			$ 23,421			$ 15,531
Notes payable 0.00% - 16.00%, due in monthly and annual installments through 2028 | Minimum
Long-Term Obligations
Interest rate on notes (as a percent)		0.00%	0.00%		0.00%	0.00%
Notes payable 0.00% - 16.00%, due in monthly and annual installments through 2028 | Maximum
Long-Term Obligations
Interest rate on notes (as a percent)		16.00%	16.00%		16.00%	16.00%
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			83			88
Long-term obligations including current maturities			$ 74,917			$ 74,912
Interest rate on notes (as a percent)		3.20%	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			172			181
Long-term obligations including current maturities			$ 124,828			$ 124,819
Interest rate on notes (as a percent)		3.50%	3.50%		3.50%	3.50%
Senior unsecured notes 0.98%, due in 2023
Long-Term Obligations
Long-term obligations gross including current maturities			$ 112,165			$ 114,535
Deferred Finance Costs, Net, Total			408			432
Long-term obligations including current maturities			$ 111,757			$ 114,103
Interest rate on notes (as a percent)		1.00%	1.00%		1.00%	1.00%
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			73			76
Long-term obligations including current maturities			$ 49,927			$ 49,924
Interest rate on notes (as a percent)		3.40%	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			172			181
Long-term obligations including current maturities			$ 99,828			$ 99,819
Interest rate on notes (as a percent)		3.50%	3.50%		3.50%	3.50%
Senior unsecured notes 1.17%, due in 2024
Long-Term Obligations
Long-term obligations gross including current maturities			$ 224,330			$ 229,070
Deferred Finance Costs, Net, Total			863			904
Long-term obligations including current maturities			$ 223,467			$ 228,166
Interest rate on notes (as a percent)		1.20%	1.20%		1.20%	1.20%
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			200			207
Long-term obligations including current maturities			$ 124,800			$ 124,793
Interest rate on notes (as a percent)		3.60%	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			200			208
Long-term obligations including current maturities			$ 124,800			$ 124,792
Interest rate on notes (as a percent)		3.60%	3.60%		3.60%	3.60%
Financial lease liabilities
Long-Term Obligations
Long-term obligations gross including current maturities			$ 23,801
Long-term obligations including current maturities			$ 23,801
Capital lease obligations
Long-Term Obligations
Long-term obligations gross including current maturities						$ 8,353
Long-term obligations including current maturities						$ 8,353