Long-term debt outstanding (Details 4) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Long-term debt maturities [Abstract]
2015	$ 269,400,000
2016	293,800,000
2017	51,000,000
2018	148,200,000
2019	345,700,000
Thereafter	986,600,000
Senior notes [Member]
Long term debt outstanding [Abstract]
Weighted average interest rate	5.43%
Commercial paper [Member]
Long term debt outstanding [Abstract]
Weighted average interest rate	0.37%
Term loan agreements [Member]
Long term debt outstanding [Abstract]
Weighted average interest rate	2.12%
Medium-term notes [Member]
Long term debt outstanding [Abstract]
Weighted average interest rate	7.32%
Other notes [Member]
Long term debt outstanding [Abstract]
Weighted average interest rate	5.23%
Loans payable [Member]
Long term debt outstanding [Abstract]
Weighted average interest rate	3.47%
Long-term debt [Member]
Long term debt outstanding [Abstract]
Long-term debt	2,094,727,000	1,854,563,000
Less current maturities	269,449,000	12,277,000
Long-term debt	1,825,278,000	1,842,286,000
Long-term debt [Member] \| Senior notes [Member]
Long term debt outstanding [Abstract]
Long-term debt	1,636,662,000	1,545,078,000
Long-term debt [Member] \| Commercial paper [Member]
Long term debt outstanding [Abstract]
Long-term debt	288,500,000	153,924,000
Long-term debt [Member] \| Term loan agreements [Member]
Long term debt outstanding [Abstract]
Long-term debt	72,000,000	75,000,000
Long-term debt [Member] \| Medium-term notes [Member]
Long term debt outstanding [Abstract]
Long-term debt	35,000,000	35,000,000
Long-term debt [Member] \| Other notes [Member]
Long term debt outstanding [Abstract]
Long-term debt	39,662,000	39,863,000
Long-term debt [Member] \| Loans payable [Member]
Long term debt outstanding [Abstract]
Long-term debt	22,939,000	5,701,000
Long-term debt [Member] \| Discount on commercial paper program [Member]
Long term debt outstanding [Abstract]
Long-term debt	$ (36,000)	$ (3,000)

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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