Earnings Per Share

Basic net income per share (“EPS”) is calculated by dividing net income attributable to common stockholders by the weighted average shares outstanding during the period. Diluted EPS is calculated by adjusting weighted average shares outstanding for the dilutive effect of potential common shares, determined using the treasury-stock method. For purposes of the diluted EPS calculation, stock options, restricted stock and restricted stock unit awards are considered to be potential common shares. Performance-based restricted stock units are not included in the calculation of diluted EPS until they are contingently issuable.

The basic and diluted EPS calculations for the three months ended March 31, 2019 and 2018 are presented below:



	Three Months Ended March 31,
(in thousands, except per share amounts)	2019		2018
Income attributable to common stockholders	$	20,350	$	15,359

Weighted average common shares outstanding, basic	66,782		67,138
Effect of dilutive securities:
Restricted stock units	415		299
Stock options	85		172
Restricted stock	—		55
Weighted average common shares outstanding, diluted	67,282		67,664

Basic income per common share	$	0.30	$	0.23
Diluted income per common share	$	0.30	$	0.23

The following table provides the securities that could potentially dilute EPS in the future, but were not included in the computation of diluted EPS for the periods presented because to do so would have been anti-dilutive. The amounts included in this table exclude performance-based restricted stock units. As of March 31, 2019, the number of currently outstanding performance-based restricted stock units that are issued upon vesting could range from zero to a maximum of 0.9 million.



	Three Months Ended March 31,
(in thousands)	2019	2018
Stock options	212	—
Restricted stock units	383	21