Employee Retirement Plan (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Retirement Plan [Abstract]
Number of days of continuous service for eligibility to participate in defined contribution benefit plan	30 days
Maximum contribution percentage of employee salary	15.00%
Percentage of employee contribution matched by Board of Directors	50.00%
Maximum percentage of each participant’s compensation	6.00%
Employee eligibility period for matching contribution (years)	1 year
Company contributions	$ 5.3	$ 4.7	$ 4.4

The maximum percentage of an employee's salary that they may contribute to the retirement plan.

No definition available.

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- Definition

Number of days of continuous service for eligibility to participate in retirement plan.

+ References

No definition available.

+ Details

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- Definition

The amount of employer contribution to the employee retirement plan based on a percentage of each employee’s contributions.

+ References

No definition available.

+ Details

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- Definition

The maximum rate of contribution to the retirement plan as a percentage of employees earnings.

+ References

No definition available.

+ Details

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- Definition

Retirement plan employee eligibility period for matching contribution.

+ References

No definition available.

+ Details

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- Details

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- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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