Stock-based compensation - Valuation Assumptions (Details) |
Apr. 09, 2015 |
Jan. 05, 2015 |
Oct. 16, 2014 |
Oct. 02, 2014 |
Feb. 01, 2014 |
|---|---|---|---|---|---|
| Disclosure of Compensation Related Costs, Share-based Payments [Abstract] | |||||
| Risk-free Interest Rate | 1.40% | 1.57% | 1.70% | 1.70% | 1.49% |
| Dividend Yield | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% |
| Stock Volatility | 37.79% | 37.74% | 37.51% | 36.63% | 32.16% |
| Option Term (years) | 10 years | 10 years | 10 years | 10 years | 5 years |
| X | ||||||||||
- References No definition available.
|
| 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
|
| X | ||||||||||
- Definition 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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|