| | | | | | | | | | | | | | | | | | | | | | | | | | |
| | Three Months Ended
September 30, | | Nine Months Ended
September 30, |
| (In millions, except per share amounts) | | 2020 | | 2019 | | 2020 | | 2019 |
| Basic Net Earnings Per Common Share: | | | | | | | | |
| Numerator: | | | | | | | | |
| Net earnings | | $ | 134.0 | | | $ | 68.0 | | | $ | 360.7 | | | $ | 158.7 | |
| Distributed and allocated undistributed net earnings to unvested restricted stockholders | | — | | | (0.1) | | | (0.1) | | | (0.3) | |
| Distributed and allocated undistributed net earnings | | 134.0 | | | 67.9 | | | 360.6 | | | 158.4 | |
| Distributed net earnings - dividends paid to common stockholders | | (24.9) | | | (24.6) | | | (74.6) | | | (74.1) | |
| Allocation of undistributed net earnings to common stockholders | | $ | 109.1 | | | $ | 43.3 | | | $ | 286.0 | | | $ | 84.3 | |
| Denominator: | | | | | | | | |
| Weighted average number of common shares outstanding - basic | | 155.5 | | | 154.0 | | | 155.2 | | | 154.4 | |
| Basic net earnings per common share: | | | | | | | | |
| Distributed net earnings | | $ | 0.16 | | | $ | 0.16 | | | $ | 0.48 | | | $ | 0.48 | |
| Allocated undistributed net earnings to common stockholders | | 0.70 | | | 0.28 | | | 1.84 | | | 0.55 | |
| Basic net earnings per common share | | $ | 0.86 | | | $ | 0.44 | | | $ | 2.32 | | | $ | 1.03 | |
| Diluted Net Earnings Per Common Share: | | | | | | | | |
| Numerator: | | | | | | | | |
| Distributed and allocated undistributed net earnings | | $ | 134.0 | | | $ | 67.9 | | | $ | 360.6 | | | $ | 158.4 | |
| Add: Allocated undistributed net earnings to unvested restricted stockholders | | — | | | 0.1 | | | 0.1 | | | 0.2 | |
| Less: Undistributed net earnings reallocated to unvested restricted stockholders | | — | | | (0.1) | | | (0.1) | | | (0.2) | |
| Net earnings available to common stockholders - diluted | | $ | 134.0 | | | $ | 67.9 | | | $ | 360.6 | | | $ | 158.4 | |
| Denominator: | | | | | | | | |
| Weighted average number of common shares outstanding - basic | | 155.5 | | | 154.0 | | | 155.2 | | | 154.4 | |
| Effect of unvested restricted stock - nonparticipating security | | 0.1 | | | — | | | 0.1 | | | — | |
| Effect of contingently issuable shares | | 0.2 | | | 0.2 | | | 0.2 | | | 0.2 | |
| Effect of unvested restricted stock units | | 0.3 | | | 0.3 | | | 0.3 | | | 0.3 | |
| Weighted average number of common shares outstanding - diluted under two-class | | 156.1 | | | 154.5 | | | 155.8 | | | 154.9 | |
| Effect of unvested restricted stock - participating security | | — | | | 0.3 | | | — | | | 0.3 | |
| Weighted average number of common shares outstanding - diluted under treasury stock | | 156.1 | | | 154.8 | | | 155.8 | | | 155.2 | |
| Diluted net earnings per common share | | $ | 0.86 | | | $ | 0.44 | | | $ | 2.31 | | | $ | 1.02 | |