Common Shares

We calculate basic earnings per common share based upon the weighted average number of common shares outstanding. We calculate diluted earnings per share based upon the weighted average number of common shares outstanding plus the dilutive effect of common share equivalents calculated using the treasury stock method. The following is a summary of common shares and common share equivalents outstanding used in the calculations of basic and diluted earnings per share:



	Three Months Ended September 30,		Six Months Ended September 30,
	2012	2011	2012	2011
Denominator (shares in thousands):
Weighted average common shares outstanding—basic	58,264	58,744	58,088	59,000
Dilutive effect of common share equivalents	528	636	464	741
Weighted average common shares outstanding and common share equivalents—diluted	58,792	59,380	58,552	59,741

Options to purchase the following number of common shares were outstanding but excluded from the computation of diluted earnings per share because the combined exercise prices, unamortized fair values, and assumed tax benefits upon exercise were greater than the average market price for the common shares during the periods, so including these options would be anti-dilutive:



	Three Months Ended September 30,		Six Months Ended September 30,
	2012	2011	2012	2011
(shares in thousands)
Number of common share options	670	585	897	445