Stock Compensation Plans (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2010 year	Sep. 30, 2011 year month segment entity plan	Sep. 30, 2010 year
Stock Compensation Plans
Weighted average volatility (as a percent)	27.80%	26.10%	28.50%
Expected dividend yield (as a percent)	1.60%	1.30%	1.60%
Risk-free rate (as a percent)	2.20%	2.20%	3.00%
Weighted average expected life (in years)	6.1	5.5	6.1
Weighted average estimated fair value per share (in dollars per share)	$ 9.13	$ 10.92	$ 10.37
Stock Options
Outstanding at beginning of period (in shares)		13,919	15,937
Granted (in shares)		80,000	143,000
Exercised (in shares)		(3,781)	(2,382)
Forfeited and expired (in shares)		(300)	(402)
Outstanding at end of period (in shares)	13,295	9,918	13,295
Exercisable (in shares)	10,535	8,566	10,535
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)		$ 32	$ 33
Granted (in dollars per share)		$ 53	$ 38
Exercised (in dollars per share)	$ 30	$ 32	$ 30
Forfeited and expired (in dollars per share)		$ 37	$ 34
Outstanding at end of period (in dollars per share)	$ 33	$ 32	$ 33
Exercisable at end of period (in dollars per share)	$ 32	$ 30	$ 32
Weighted average remaining contractual life of outstanding options (in years)		3.3	3.6

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The weighted average price at which grantees can acquire the shares reserved for issuance of stock options awarded under the plan during the reporting period.

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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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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.

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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.

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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 number of shares into which fully or partially vested stock options outstanding as of the balance-sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The weighted average period between the balance-sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years.

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The decrease in the number of reserved shares that could potentially be issued attributable to the exercise or conversion during the reporting period of previously issued stock options under the option plan.

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The weighted average price at which option holders acquired shares when converting their stock options into shares under the plan during the reporting period.

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For presentations that combine terminations, the weighted average price of expired options and the price at which grantees could have acquired the underlying shares with respect to stock options that were terminated during the reporting period due to noncompliance with plan terms during the reporting period .

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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The quantity of shares issuable on stock options awarded under the plan during the reporting period.

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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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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance-sheet date, including vested options.

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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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