The Company calculates earnings per share using the two-class method. The two-class method allocates net income to each class of common stock and participating security according to common dividends declared and participation rights in undistributed earnings. Participating securities consist of nonvested share-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents.

A summary of the information used in the computation of earnings per common share follows.

	Three Months Ended
	March 31,
(in thousands, except per share data)	2019		2018
Numerator:
Net income to common shareholders	$	79,164	$	72,475
Net income allocated to participating securities - basic and diluted		1,337		1,366
Net income allocated to common shareholders - basic and diluted	$	77,827	$	71,109
Denominator:
Weighted-average common shares - basic		85,688		85,241
Dilutive potential common shares		112		182
Weighted-average common shares - diluted		85,800		85,423
Earnings per common share:
Basic	$	0.91	$	0.83
Diluted	$	0.91	$	0.83

Potential common shares consist of stock options, nonvested performance-based awards, and nonvested restricted share awards deferred under the Company’s nonqualified deferred compensation plan. These potential common shares do not enter into the calculation of diluted earnings per share if the impact would be antidilutive, i.e., increase earnings per share or reduce a loss per share. Weighted average antidilutive potential common shares totaled 1,281 for the three months ended March 31, 2019. There were no antidilutive potential common shares excluded from the calculation of diluted earnings per share for the three months ended March 31, 2018.