| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Net income | 158.6 | 182.0 | -225.6 | -56.0 | -32.9 | -58.7 | -217.8 | -254.4 |
| Depreciation and amortization | 60.2 | 56.2 | 65.2 | 72.8 | 69.0 | 71.8 | 76.3 | 79.6 |
| Asset impairment charges | | | | | | 22.0 | 72.0 | |
| Stock-based compensation | 3.2 | 2.3 | 2.0 | 2.1 | 2.2 | 4.1 | 20.7 | |
| Change in working capital [+] | -4.7 | -5.5 | -13.0 | 23.3 | -28.4 | -13.3 | -2.8 | 2.7 |
| Accounts receivable | -5.2 | -7.1 | 0.7 | 8.6 | -10.1 | -2.5 | 0.2 | |
| Inventories | 3.0 | -3.0 | 5.6 | 2.3 | -14.2 | -6.5 | 0.8 | |
| Other current assets | -0.3 | -0.8 | -1.9 | -0.8 | -6.6 | -5.9 | 1.0 | |
| Deferred revenues | | | | | | | 0.4 | |
| Other | -2.1 | 5.4 | -17.4 | 13.2 | 2.6 | 1.5 | -5.3 | 2.7 |
| Other operating activities | -28.0 | -3.9 | 208.2 | 17.3 | 56.0 | -1.7 | -0.7 | 116.0 |
| Cash from operations | 189.3 | 231.1 | 36.9 | 59.5 | 65.9 | 24.1 | -52.3 | -56.1 |
| |
| Capital expenditures | -3.6 | -1.6 | -4.6 | -4.7 | -1.5 | -0.3 | -0.3 | 0.0 |
| Purchases of property and equipment | -3.6 | -1.6 | -4.6 | -4.7 | -1.5 | -0.3 | -0.3 | |
| Sales of short-term investments | | | | | | | 10.5 | |
| Sales of short-term investments | | | | | | | 10.5 | |
| Other cash from investing | -51.4 | -66.0 | 42.0 | -18.1 | -193.9 | 17.7 | 14.9 | -56.8 |
| Cash from investing | -55.0 | -67.6 | 37.4 | -22.8 | -195.4 | 17.4 | 25.1 | -56.8 |
| |
| Cash dividends paid | -115.7 | -13.5 | -9.8 | -20.9 | | | | |
| Issuance of common stock, net | | | | | 110.2 | | | |
| Financing costs | 0.0 | -6.1 | -0.5 | -0.6 | -11.8 | | -1.5 | |
| Other cash from financing | -75.0 | -215.3 | -47.5 | -56.9 | 5.2 | -5.6 | 53.9 | 150.5 |
| Cash from financing | -190.7 | -222.7 | -56.9 | -77.2 | 127.3 | -5.6 | 55.4 | 150.5 |
| |
| Free cash flow | 185.8 | 229.5 | 32.3 | 54.8 | 64.4 | 23.8 | -52.6 | -56.1 |
| Per share (diluted) | $4.33 | $5.39 | $0.77 | $1.31 | $1.68 | $0.69 | ($7.26) | ($0.85) |