Health care rate assumptions and cost trend rate (Details 7) (Other Postretirement Benefits, USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care trend rate assumed for next year (minimum)	6.00%	6.00%
Health care trend rate assumed for next year (maximum)	8.00%	8.00%
Health care cost trend rate - ultimate (minimum)	5.00%	5.00%
Health care cost trend rate - ultimate (maximum)	6.00%	6.00%
Year In which ultimate trend rate achieved, (maximum)	2017	2017
Percentage excess over the health care cost trend rate that retiree contributions will generally increase each year	6.00%
Effect on total of service and interest cost components, one percentage point increase	$ 340
Effect on total of service and interest cost components, one percentage point decrease	(278)
Effect on postretirement benefit obligations, one percentage point increase	5,724
Effect on postretirement benefit obligations, one percentage point decrease	$ (4,858)

The ultimate trend rate for health care costs. (maximum)

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- Definition

The ultimate trend rate for health care costs. (minimum)

+ References

No definition available.

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The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. (maximum)

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- Definition

Percentage excess over the health care cost trend rate that retiree contributions will generally increase each year.

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No definition available.

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The year when the ultimate health care cost trend rate is expected to be reached, (Maximum)

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (m)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph m

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

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