| In millions, except per share items | Aug-31-23 | May-31-23 | Aug-31-22 | May-31-22 | Feb-28-22 | Nov-30-21 | Aug-31-21 | May-31-21 |
| | 10-Q | 10-Q | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q |
| Sales | 398.5 | 390.9 | 406.7 | 207.1 | 224.7 | 231.7 | 131.4 | 229.8 |
| Sales growth | -2.0% | 88.7% | 209.4% | -9.9% | 14.8% | 2.3% | -35.4% | 7.8% |
| Costs and Expenses | | | | | | | | |
| Cost of sales | 301.3 | 293.9 | 305.2 | 147.1 | 169.4 | 174.8 | 95.0 | 171.9 |
| Gross margin | 97.2 | 97.0 | 101.6 | 60.1 | 55.2 | 57.0 | 36.4 | 57.9 |
| Gross margin | 24.4% | 24.8% | 25.0% | 29.0% | 24.6% | 24.6% | 27.7% | 25.2% |
| Selling, general and administrative | 36.2 | 31.5 | 37.4 | 32.1 | 31.0 | 26.9 | 16.5 | 27.2 |
| Operating income from continuing operations | 61.0 | 65.5 | 64.1 | 27.9 | 26.0 | 30.1 | 20.0 | 30.7 |
| Operating margin | 15.3% | 16.8% | 15.8% | 13.5% | 11.6% | 13.0% | 15.2% | 13.4% |
| Interest expense | -27.8 | -28.7 | -28.1 | -7.5 | -1.3 | -1.6 | -1.7 | -1.7 |
| Equity in (earnings) loss of unconsolidated subsidiaries | -1.0 | -1.4 | | | | | | |
| Other (income) expense, net | -0.1 | 0.0 | 0.1 | 0.0 | -0.8 | 1.4 | 0.0 | -1.0 |
| Income from continuing operations before income taxes | 34.3 | 38.2 | 35.9 | 20.5 | | | 18.2 | |
| Income tax expense | 6.0 | 9.7 | 10.8 | 5.1 | 3.8 | 6.0 | 3.9 | 7.6 |
| Net income from continuing operations | 28.3 | 28.5 | 25.1 | 15.4 | | | 14.3 | |
| Income from discontinued operations, net of tax | | | 6.7 | 8.7 | | | 4.7 | |
| Loss on disposal of discontinued operations, net of tax | | | -89.4 | 8.7 | | | | |
| Net income (loss) from discontinued operations | | | -82.7 | 8.7 | | | 4.7 | |
| Net income (loss) | 28.3 | 28.5 | -57.6 | 24.1 | 21.6 | 21.1 | 19.0 | 22.3 |
| Dividends on preferred stock | -3.6 | -3.6 | -1.0 | | | | | |
| Net income (loss) available to common shareholders | 24.7 | 24.9 | -58.6 | 24.1 | | | 19.0 | |
| |
| Basic earnings (loss) per share | | | | | | | | |
| Earnings | 0.0 | 0.0 | 0.0 | 0.0 | | | 0.0 | |
| Earnings | | | 0.0 | 0.0 | | | 0.0 | |
| |
| Basic earnings per common share (usd per share) | $0.99 | $1.00 | ($2.36) | $0.97 | $0.87 | $0.85 | $0.76 | $0.89 |
| |
| Diluted Earnings (Loss) Per Share [Abstract] | | | | | | | | |
| Diluted earnings per common share (usd per share) | $0.97 | $0.98 | ($1.91) | $0.96 | $0.87 | $0.85 | $0.76 | $0.88 |
| Earnings | 0.0 | 0.0 | 0.0 | 0.0 | | | 0.0 | |
| Earnings | | | 0.0 | 0.0 | | | 0.0 | |
| |
| Weighted average shares outstanding | | | | | | | | |
| Weighted average number common shares, basic (shares) | 25.1 | 24.9 | 24.8 | 24.7 | 24.9 | 24.7 | 0.0 | 25.1 |
| Weighted average number common shares, diluted (shares) | 29.2 | 29.2 | 29.1 | 25.7 | 25.1 | 24.9 | 0.0 | 25.3 |
| |
| Cash dividends declared per common share (usd per share) | $0.17 | $0.17 | $0.17 | $0.17 | $0.17 | $0.17 | $0.17 | $0.17 |