- DefinitionThe 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://fasb.org/us-gaap/role/ref/legacyRef
 -Publisher FASB
 -Name Accounting Standards Codification
 -Topic 718
 -SubTopic 10
 -Section 50
 -Paragraph 2
 -Subparagraph (f)(2)(ii)
 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901
| Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate | 
| Namespace Prefix: | us-gaap_ | 
| Data Type: | num:percentItemType | 
| Balance Type: | na | 
| Period Type: | duration |