Note 14. Earnings Per Share

Earnings per share is calculated 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 unvested 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:



	Years Ended December 31,
($ in thousands, except per share data)	2018		2017		2016
Numerator:
Net income to common shareholders	$	323,770	$	215,632	$	149,296
Net income allocated to participating securities -- basic and diluted		5,930		4,670		3,598
Net income allocated to common shareholders - basic and diluted	$	317,840	$	210,962	$	145,698
Denominator:
Weighted-average common shares - basic		85,355		84,695		77,850
Dilutive potential common shares		166		268		99
Weighted average common shares - diluted		85,521		84,963		77,949
Earnings per common share:
Basic	$	3.72	$	2.49	$	1.87
Diluted	$	3.72	$	2.48	$	1.87

Potential common shares consist of employee and director stock options, unvested performance share awards, and deferred restricted units. These potential common shares do not enter into the calculation of diluted earnings per share if the impact would be anti-dilutive, i.e., increase earnings per share or reduce a loss per share. Weighted-average anti-dilutive potential common shares totaled 5,129 for the year ended December 31, 2018, 10,551 for the year ended December 31, 2017, and 572,512 for the year ended December 31, 2016.