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Summary of Significant Accounting Policies Fair Value Calculation Assumptions (Details) (Market share units)	3 Months Ended
	Jun. 30, 2013
Market share units
Valuation Assumptions for MSUs [Line Items]
Volatility	57.00%
Risk-free interest rate	0.35%
Expected life, in years	2 years 10 months 2 days
Dividend yield	0.00%

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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