|
Stock-based compensation Stock-based compensation (Details 4) (Performance Units [Member], USD $)
|
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2012
|
Dec. 31, 2011
|
Dec. 31, 2010
|
|
|
Performance Units [Member]
|
|||
| Weighted-average assumptions and resulting weighted-average grant date fair values [Abstract] | |||
| Closing price of our common stock on grant date | $ 68.75 | $ 51.67 | $ 56.90 |
| Expected volatility | 22.90% | 32.80% | 34.70% |
| Risk-free interest rate | 0.50% | 1.20% | 1.30% |
| Expected dividend yield | 2.20% | 0.10% | 0.00% |
| Fair value of unit (in usd per share) | $ 78.21 | $ 49.50 | $ 62.06 |
| X | ||||||||||
|
- Definition
The closing price of our common stock on grant date used to estimate the grant date fair value of our stock-based compensation. No definition available.
|
| X | ||||||||||
|
- Definition
The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
|
- Details
|
| X | ||||||||||
|
- 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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
|
- Definition
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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
|
- Definition
The risk-free interest rate assumption that is used in valuing an option on its own shares. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|