Note 13. Earnings per Share

Basic earnings per share is computed by dividing net income attributable to our stockholders by the weighted average number of shares of common stock and vested deferred stock units outstanding during the year. The computation of diluted earnings per share is similar to the computation of basic earnings per share, except that the denominator is increased for the assumed exercise of dilutive options and assumed issuance of unvested restricted stock units and unvested deferred stock units using the treasury stock method unless the effect is anti-dilutive. The treasury stock method assumes that proceeds, including cash received from the exercise of employee stock options and the total unrecognized compensation expense for unvested share-based compensation awards would be used to purchase our common stock at the average market price during the period. Vested deferred stock units outstanding are included in shares outstanding for basic and diluted earnings per share because the associated shares of our common stock are issuable for no cash consideration, the number of shares of our common stock to be issued is fixed and issuance is not contingent. See Note 4 to the consolidated financial statements in our 2017 Annual Report for additional information regarding deferred stock units.

The following is a reconciliation of weighted average shares outstanding for basic and diluted earnings per share for the three months ended March 31, 2018 and 2017 (in thousands):


	For the Three Months Ended
	March 31,
	2018	2017

Shares outstanding for basic earnings per share	87,331	88,117

Shares outstanding for diluted earnings per share:
Shares outstanding for basic earnings per share	87,331	88,117
Dilutive effect of share-based payment awards	1,613	1,877
	88,944	89,994

Certain options to acquire shares and restricted stock units have been excluded from the calculation of shares outstanding for diluted earnings per share because they were anti-dilutive. The following table presents information concerning those anti-dilutive options and restricted stock units for the three months ended March 31, 2018 and 2017 (in thousands):


	For the Three Months Ended
	March 31,
	2018	2017

Weighted average number of shares underlying anti-dilutive options	167	182

Weighted average number of shares underlying anti-dilutive restricted stock units	-	47