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.

	Years Ended December 31,
($ in thousands, except per share data)	2019		2018		2017
Numerator:
Net income to common shareholders	$	327,380	$	323,770	$	215,632
Net income allocated to participating securities -- basic and diluted		5,546		5,930		4,670
Net income allocated to common shareholders - basic and diluted	$	321,834	$	317,840	$	210,962
Denominator:
Weighted-average common shares - basic		86,488		85,355		84,695
Dilutive potential common shares		111		166		268
Weighted average common shares - diluted		86,599		85,521		84,963
Earnings per common share:
Basic	$	3.72	$	3.72	$	2.49
Diluted	$	3.72	$	3.72	$	2.48

Potential common shares are excluded from the computation of diluted earnings per share when their inclusion would have had an anti-dilutive effect. Potential common shares can consist of, among other forms, employee and director stock options, unvested performance share awards, and deferred restricted units. Weighted-average anti-dilutive potential common shares of this nature totaled 15,815 for the year ended December 31, 2019, 5,129 for the year ended December 31, 2018, and 10,551 for the year ended December 31, 2017.

The diluted earnings per share computation for the year ended December 31, 2019 also excludes the impact of the forward contract related to the October 21, 2019 accelerated share repurchase transaction. Based upon the average daily volume weighted-average price of the Company’s common stock at December 31, 2019, the counterparty to the transaction is expected to deliver additional shares for the settlement of the forward contract upon settlement; as such, the impact of the forward contract related to the accelerated share repurchase transaction would have been anti-dilutive to earnings per share.