Long-term debt outstanding (Details 3) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Long term debt outstanding [Abstract]
Long-term debt	$ 2,108,695	$ 1,714,853
Long-term debt due within one year	251,854	148,499
Long-term debt	$ 1,856,841	1,566,354
Senior notes
Long term debt outstanding [Abstract]
Weighted average interest rate	4.57%
Long-term debt	$ 1,381,000	1,499,916
Commercial paper
Long term debt outstanding [Abstract]
Weighted average interest rate	3.10%
Long-term debt	$ 338,100	88,350
Term Loan Agreements
Long term debt outstanding [Abstract]
Weighted average interest rate	2.75%
Long-term debt	$ 209,800	0
Credit agreements
Long term debt outstanding [Abstract]
Weighted average interest rate	4.40%
Long-term debt	$ 110,100	57,300
Medium-term notes
Long term debt outstanding [Abstract]
Weighted average interest rate	6.68%
Long-term debt	$ 50,000	50,000
Other notes
Long term debt outstanding [Abstract]
Weighted average interest rate	5.22%
Long-term debt	$ 25,229	24,982
Long-term debt
Long term debt outstanding [Abstract]
Unamortized debt issuance costs	5,207	5,694
Discount	$ 327	$ 1

Amount, after accumulated amortization, of debt discount.

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