Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Performance stock awards [Member]
Fair value of stock options, performance stock awards and shares purchasable under ESPP
Risk-free interest rate	0.00%		1.30%
Volatility	0.00%		33.40%
Dividend yield	0.00%		0.00%
Expected term (years)	0		2.9
Resulting average fair value	$ 0		$ 42.66
Employee Stock [Member]
Fair value of stock options, performance stock awards and shares purchasable under ESPP
Risk-free interest rate	0.20%	0.20%	0.20%	0.20%
Volatility	21.50%	26.50%	21.50%	26.50%
Dividend yield	0.00%		0.00%
Expected term (years)	0.5	0.5	0.5	0.5
Resulting average fair value	$ 12.27	$ 9.65	$ 12.27	$ 9.65
Employee Stock Option [Member]
Fair value of stock options, performance stock awards and shares purchasable under ESPP
Risk-free interest rate	1.90%	2.10%	1.70%	2.10%
Volatility	30.20%	31.40%	30.90%	32.10%
Dividend yield	0.00%		0.00%
Expected term (years)	4.3	4.4	4.3	4.4
Resulting average fair value	$ 22.35	$ 13.52	$ 18.05	$ 12.74

The weighted average fair value at grant for nonvested share-based awards issued during the period on other than stock option plans (for example, phantom stock plan, stock appreciation rights plan, performance target plan).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(2)(c)

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph c(1)

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph e(2)(c)

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- Definition

The period of time a share-based award is expected to be outstanding. A share-based award's expected term shall be determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior. An entity is required to aggregate individual awards into relatively homogeneous groups.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph e(2)(a)

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14
-Section D
-Subsection 2

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- Definition

The estimated measure of the percentage amount by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph e(2)(b)

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph e(2)(d)

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