Retirement Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Retirement Plan [Line Items]
Number of qualified defined contribution plans	1
Contributions to ESOP	$ 23.8	$ 22.9	$ 22.0
ESOP vesting period in years	5 years
ESOP Compensation expense	3.6	3.4	3.0
Unearned ESOP shares	0	0
ESSP qualified annual base compensation deferral amount	75.00%
ESSP qualified bonus deferral amount	100.00%
ESSP participant contributions	4.5	4.2	4.3
Rabbi trust assets invested in money market account	100.00%	100.00%
Benefit obligation for define benefit pension plan	$ 1.5	$ 1.5
Common Class A [Member]
Retirement Plan [Line Items]
Shares contributed to ESOP	116,087	81,730	84,991

Deferred Compensation Arrangement with Individual, Employee Contribution

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- Definition

Employee Stock Ownership Plan (ESOP), Unearned ESOP Shares

+ References

No definition available.

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- Definition

Employee Stock Ownership Plan (ESOP), Vesting Period

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- Definition

The maximum percentage of qualified annual base compensation that can be deferred by eligible employees under the Employee Supplemental Savings Plan.

+ References

No definition available.

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- Definition

The maximum percentage of bonus that can be deferred by eligible employees under the Employee Supplemental Savings Plan.

+ References

No definition available.

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- Definition

Number of Qualified Defined Contribution Plans

+ References

No definition available.

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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. 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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Projected Benefit Obligation

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Accumulated Postretirement Benefit Obligation

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph 5

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- Definition

The percentage of the fair value of investments other than debt securities, equity securities, and real estate to the fair value of total plan assets held as of the measurement date.

+ References

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-Publisher FASB

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-Number 132R

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- Definition

The amount of the cost recognized during the period for defined contribution plans.

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-Number 132R

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- Definition

The amount of plan compensation cost recognized during the period.

+ References

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-Publisher AICPA

-Name Statement of Position (SOP)

-Number 93-6

-Paragraph 53

-Subparagraph c

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- Definition

This item represents the number of shares provided to the Employee Stock Ownership Plan (ESOP) during the period.

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-Publisher AICPA

-Name Statement of Position (SOP)

-Number 93-6

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