DEBT (Details) € in Thousands, $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 USD ($)
Long-Term Obligations
Consolidated Leverage Ratio						2.09	2.09
Consolidated Interest Coverage Ratio						14.57	14.57
Long-term obligations gross including current maturities							$ 1,191,489		$ 1,256,375
Current maturities of long-term obligations							(62,678)		(61,833)
Total long-term obligations							1,128,811		1,194,542
Deferred Finance Costs, Net, Total							2,818		3,396
Deferred debt issuance costs noncurrent							2,818		3,396
Long-term obligations including current maturities							1,188,671		1,252,979
Current maturities of long-term obligations							(62,678)		(61,833)
Long-term obligations, net of unamortized debt issuance costs							1,125,993		1,191,146
Aggregate long-term maturities, excluding capital lease obligations
2019							61,350
2020							60,045
2021							59,116
2022							133,068
2023							239,889
Thereafter							$ 629,668
Minimum
Long-Term Obligations
Consolidated Interest Coverage Ratio						3.00	3.00
Maximum
Long-Term Obligations
Consolidated Leverage Ratio						3.50	3.50
Unsecured lines of credit
Long-Term Obligations
Average borrowings				$ 40,000	$ 64,500
Average annual interest rate on short-term notes payable (as a percent)				1.90%	1.90%
Revolving credit facility
Long-Term Obligations
Amount outstanding under line of credit						€ 69,000	$ 79,000	€ 0	0
Credit facility interest and fees				$ 1,500	$ 1,500
Proceeds from debt | €		€ 150,000
Term of debt		5 years	5 years
Interest rate on notes (as a percent)		1.10%	1.10%
5-year revolving credit facility maturing in July 2022
Long-Term Obligations
Revolving credit facility maximum borrowing capacity							300,000
Amount outstanding under line of credit							0
Term of debt				5 years
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							541		692
Long-term obligations including current maturities							$ 223,459		279,308
Interest rate on notes (as a percent)		1.36%	1.36%
Floating interest rate prior to conversion to a fixed interest rate		2.62%	2.62%			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							$ 15,531		15,349
Long-term obligations including current maturities							$ 15,531		$ 15,349
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%	0.61%	0.61%
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%	18.00%	18.00%
Senior unsecured notes 6.0%, due in 2018
Long-Term Obligations
Debt prepayment amount	$ 75,000
Interest rate on notes (as a percent)								6.00%	6.00%
Senior unsecured notes 3.8%, due in 2020
Long-Term Obligations
Debt prepayment amount	$ 84,000
Interest rate on notes (as a percent)								3.80%	3.80%
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							88		113
Long-term obligations including current maturities							$ 74,912		$ 74,887
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							181		217
Long-term obligations including current maturities							$ 124,819		$ 124,783
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
Proceeds from private placement | €		€ 100,000
Term of debt		6 years	6 years
Long-term obligations gross including current maturities							$ 114,535		$ 120,095
Deferred Finance Costs, Net, Total							432		526
Long-term obligations including current maturities							114,103		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							76		89
Long-term obligations including current maturities							$ 49,924		$ 49,911
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							181		217
Long-term obligations including current maturities							$ 99,819		$ 99,783
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
Proceeds from private placement | €		€ 200,000
Term of debt		7 years	7 years
Long-term obligations gross including current maturities							$ 229,070		$ 240,190
Deferred Finance Costs, Net, Total							904		1,066
Long-term obligations including current maturities							228,166		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							207		238
Long-term obligations including current maturities							$ 124,793		$ 124,762
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							208		238
Long-term obligations including current maturities							$ 124,792		$ 124,762
Interest rate on notes (as a percent)						3.60%	3.60%	3.60%	3.60%
Capital lease obligations
Long-Term Obligations
Long-term obligations gross including current maturities							$ 8,353		$ 741
Long-term obligations including current maturities							$ 8,353		$ 741