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Long-term debt outstanding (Details 3) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
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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

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