Earnings Per Share

12 Months Ended

Dec. 31, 2017

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)	2017		2016		2015
Numerator:
Net income to common shareholders	$	215,632	$	149,296	$	131,461
Net income allocated to participating securities -- basic and diluted		4,670		3,598		2,895
Net income allocated to common shareholders - basic and diluted	$	210,962	$	145,698	$	128,566
Denominator:
Weighted-average common shares - basic		84,695		77,850		78,197
Dilutive potential common shares		268		99		110
Weighted average common shares - diluted		84,963		77,949		78,307
Earnings per common share:
Basic	$	2.49	$	1.87	$	1.64
Diluted	$	2.48	$	1.87	$	1.64

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 10,551 for the year ended December 31, 2017, 572,512 for the year ended December 31, 2016, and 798,623 for the year ended December 31, 2015.