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Summary of Significant Accounting Policies (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity Incentive Plans [Member]
Options granted under the equity incentive plans and shares subject to the employee stock purchase plan valuation assumptions
Average risk-free interest rate	0.85%	1.25%	1.93%
Expected dividend yield	1.70%
Expected life	4 years 6 months	3 years 6 months	3 years 7 months 6 days
Expected volatility	40.00%	40.00%	40.00%
Weighted average fair value	$ 9.64	$ 10.47	$ 9.67
Employee Stock Purchase Plan [Member]
Options granted under the equity incentive plans and shares subject to the employee stock purchase plan valuation assumptions
Average risk-free interest rate	0.14%	0.13%	0.17%
Expected dividend yield	1.70%
Expected life	6 months	6 months	6 months
Expected volatility	31.00%	28.00%	25.00%
Weighted average fair value	$ 6.90	$ 7.55	$ 6.38

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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.

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-Name Accounting Standards Codification

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-Name Staff Accounting Bulletin (SAB)

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The estimated measure of the percentage 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.

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

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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