Employee Benefit Plan Obligations (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Change in plan assets
Fair value of plan assets at beginning of year	$ 84,097
Company contributions	5,000
Fair value of plan assets at end of year	87,605
Pension Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	90,603	74,875
Service cost		1,614	2,861
Interest cost	4,578	4,339	4,001
Actuarial (gains)/losses	16,363	12,120
Benefits paid	(1,568)	(2,345)
Benefit obligation at end of year	109,976	90,603	74,875
Change in plan assets
Fair value of plan assets at beginning of year	84,097	70,423
Actual gains (loss) on plan assets	(91)	9,852
Company contributions	5,167	6,167
Benefits paid	(1,568)	(2,345)
Fair value of plan assets at end of year	87,605	84,097	70,423
Funded status of plans at end of year	(22,371)	(6,506)
Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	24,593	21,294
Service cost	555	465	412
Interest cost	1,285	1,213	1,155
Actuarial (gains)/losses	6,020	2,383
Participant contributions	478	444
Retiree drug subsidy received	202	118
Benefits paid	(1,575)	(1,324)
Benefit obligation at end of year	31,558	24,593	21,294
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Company contributions	1,097	880
Participant contributions	478	444
Benefits paid	(1,575)	(1,324)
Fair value of plan assets at end of year	0	0	0
Funded status of plans at end of year	$ (31,558)	$ (24,593)

The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(iv)(b)(i)

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 106

-Paragraph 518

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 264

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

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- Definition

The net increase or decrease of changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 106

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

-Publisher FASB

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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- Definition

1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. The projected benefit obligation is measured using assumptions as to future compensation levels if the pension benefit formula is based on those future compensation levels (pay-related, final-pay, final-average-pay, or career-average-pay plans). For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date. Prior to an employee's full eligibility date, the accumulated postretirement benefit obligation as of a particular date for an employee is the portion of the expected postretirement benefit obligation attributed to that employee's service rendered to that date; on and after the full eligibility date, the accumulated and expected postretirement benefit obligations for an employee are the same.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph a

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 6

-Subparagraph a

Reference 3: http://www.xbrl.org/2003/role/presentationRef

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph a, b

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-Number 87

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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- Definition

The amount of contributions made by the employer.

+ References

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

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The amount of contributions made by plan participants. Under a contributory plan active employees or retirees contribute part of the cost. In some contributory plans, those wishing to be covered must contribute; in others, the contributions result in increased benefits.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those nonbenefit obligations may be considered as reductions of plan assets.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph b

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

+ References

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

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Amount of the period's gross receipts received from the prescription drug subsidy, which is to be used in the roll forward of the accumulated postretirement benefit obligation of an applicable postretirement benefit plan.

+ References

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

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-Name FASB Staff Position (FSP)

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- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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