Basic net income per common share is calculated by dividing net income by the weighted average number of common shares outstanding during the period. Diluted net income per common share is calculated by dividing net income by the weighted average number of common and potential common shares outstanding during the period. Potential common shares consist of outstanding restricted and deferred stock and stock options calculated using the treasury stock method. Under the treasury stock method, the Company includes the assumed excess tax benefits related to the potential exercise or vesting of its stock-based awards using the difference between the average market price for the applicable period less the option price, if any, and the fair value of the stock-based award on the date of grant multiplied by the applicable tax rate.

The calculation of shares used in the basic and diluted net income per common share calculation for the three months ended March 31, 2015 and 2014 is as follows (in thousands):