Cash flow information (Details 1) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015
Supplemental Cash Flow Information [Abstract]
Interest, net of amounts capitalized and AFUDC - borrowed of $548 and $4,481 in 2016 and 2015, respectively	$ 44,860	$ 44,564
Capitalized interest and AFUDC borrowed	548	4,481
Income taxes paid, net	29,891	7,147
Property, plant and equipment additions in accounts payable	$ 18,449	$ 11,576

Future cash outflow to pay for purchases of fixed assets that have occurred.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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- Definition

The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4297-108586

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- Definition

Amount of interest capitalized, including amount of allowance for funds used during construction.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Allowance for Funds Used during Construction
-URI http://asc.fasb.org/extlink&oid=6504829

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

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- Definition

The amount of cash paid for interest during the period net of cash paid for interest that is capitalized.

+ References

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- References

No definition available.

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