9. Earnings Per Share

Basic earnings per common share is calculated by dividing net income available to common stockholders by the weighted average number of common shares outstanding for the period. Diluted earnings per common share reflects the assumed conversion of all potentially dilutive securities, consisting of stock options and restricted stock awards, for which the estimated fair value exceeds the exercise price, less shares which could have been purchased with the related proceeds, unless anti-dilutive. For employee equity awards, repurchased shares are also included for any unearned compensation adjusted for tax. The table below reflects the calculation of the weighted average number of common shares outstanding, on an as if converted basis, used in computing basic and diluted earnings per common share.


	Year Ended December 31,
	2017		2016		2015
Denominator:
Basic weighted average shares outstanding		47,140		46,083		45,975
Effect of dilutive stock options and restricted stock		1,095		1,038		1,306

Diluted weighted average shares outstanding		48,235		47,121		47,281

Diluted weighted average shares outstanding excludes the incremental effect of unvested restricted stock and shares that would be issued upon the assumed exercise of stock options in accordance with the treasury stock method. For each of the years ended December 31, 2017, 2016 and 2015, approximately 2, 344 and 385, respectively, of the University’s stock options and restricted stock awards outstanding were excluded from the calculation of diluted earnings per share as their inclusion would have been anti-dilutive. These options and restricted stock awards could be dilutive in the future.