| Schedule of Earnings Per Share, Basic and Diluted |
The following table summarizes the average number of common shares and the net income used in the calculation of basic and diluted earnings per common share ($ in thousands, except share and per share amounts): | | | | | | | | | | | | | | | | | | | Year Ended December 31, | | 2020 | | 2019 | | 2018 | | Net income attributable to common stockholders | $ | 185,126 | | | $ | 160,456 | | | $ | 154,333 | | | | | | | | | BASIC: | | | | | | | Weighted average common shares outstanding | 44,696,285 | | | 43,417,828 | | | 41,943,873 | | | | | | | | | DILUTED: | | | | | | | Weighted average common shares outstanding | 44,696,285 | | | 43,417,828 | | | 41,943,873 | | | Stock options | 1,719 | | | 75,196 | | | 67,735 | | | Convertible subordinated debentures | — | | | 210,224 | | | 80,123 | | | Weighted average dilutive common shares outstanding | 44,698,004 | | | 43,703,248 | | | 42,091,731 | | | | | | | | | Net income attributable to common stockholders - basic | $ | 4.14 | | | $ | 3.70 | | | $ | 3.68 | | | Net income attributable to common stockholders - diluted | $ | 4.14 | | | $ | 3.67 | | | $ | 3.67 | | | | | | | | | Incremental anti-dilutive shares excluded: | | | | | | | Net share effect of stock options with an exercise price in excess of the | | | | | | | average market price for our common shares | 390,596 | | | 4,678 | | | 518 | | | | | | | | | Regular dividends declared per common share | $ | 4.41 | | | $ | 4.20 | | | $ | 4.00 | |
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