| In millions, except per share items | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| CASH FLOWS FROM OPERATING ACTIVITIES: | | | | | | | |
| Net income | 90.4 | 32.8 | 4.9 | 38.5 | 131.6 | 40.5 | 13.5 |
| Adjustments to reconcile net income to net cash from operating activities: | | | | | | | |
| Depreciation | 11.1 | 12.6 | 13.6 | 12.3 | 9.2 | 4.6 | 2.7 |
| Stock-based compensation | 33.7 | 35.2 | 29.6 | 23.4 | 20.7 | 0.8 | 0.4 |
| Deferred income taxes | 2.7 | -13.1 | 3.1 | -18.4 | -12.3 | -11.2 | |
| Non-cash lease expense | 4.6 | 4.9 | | | | | |
| Other non-cash charges (benefits) | 0.8 | -2.2 | -0.8 | 0.4 | 0.1 | | |
| Changes in operating assets and liabilities: | | | | | | | |
| Accounts receivable | -20.5 | -7.1 | -4.2 | 21.5 | -66.9 | -23.2 | -6.0 |
| Inventory | 2.8 | -15.3 | 36.7 | -30.6 | -3.8 | -12.9 | 1.1 |
| Prepaid expenses and other current assets | -1.5 | 6.1 | 6.2 | -6.5 | -10.9 | 1.1 | -2.1 |
| Other assets | 0.0 | -0.3 | 1.1 | -4.6 | -0.6 | -0.1 | 0.0 |
| Accounts payable | 15.3 | -0.8 | 1.4 | -2.4 | 23.3 | 11.9 | 1.7 |
| Accrued liabilities | -0.2 | 26.8 | -5.5 | 7.0 | 14.4 | 6.7 | 0.2 |
| Deferred revenue | -2.2 | -0.9 | 8.4 | -0.5 | -6.4 | | |
| Income taxes payable | -0.8 | -1.7 | -12.2 | 21.0 | | | |
| Lease liabilities | -5.2 | -4.5 | | | | | |
| Other long-term liabilities | 0.1 | 0.6 | 0.7 | 0.8 | 1.1 | 0.4 | |
| Net cash provided by operating activities | 131.1 | 72.8 | 83.1 | 61.9 | 102.8 | 22.5 | 13.4 |
| |
| CASH FLOWS FROM INVESTING ACTIVITIES: | | | | | | | |
| Purchases of property and equipment | -12.9 | -11.8 | -14.7 | -14.1 | -17.3 | -12.1 | -6.5 |
| Purchases of marketable securities | -418.9 | -476.2 | -382.4 | -436.6 | -118.7 | | |
| Sales and maturities of marketable securities | 383.7 | 384.5 | 340.9 | 242.7 | 14.5 | | |
| Deposits | | | | | | | |
| Net cash used in investing activities | -48.2 | -103.6 | -56.2 | -207.9 | -121.5 | -12.1 | -6.5 |
| |
| CASH FLOWS FROM FINANCING ACTIVITIES: | | | | | | | |
| Treasury stock acquired | | | -39.7 | | | | |
| Proceeds from the issuance of common stock under stock-based compensation plans | 2.2 | 6.9 | 5.8 | 5.7 | 2.6 | 0.2 | 0.1 |
| Net cash provided by (used in) financing activities | 2.2 | 6.9 | -33.9 | 5.5 | 199.1 | -3.8 | -6.0 |
| Net increase (decrease) in cash and cash equivalents | 85.1 | -23.8 | -7.1 | | | | |
| |
| Supplemental cash flow disclosures: | | | | | | | |
| Cash paid (refunds received) for income taxes, net | 3.1 | -0.1 | -5.1 | 1.5 | 3.1 | 7.3 | 4.7 |
| Supplemental disclosure of non-cash investing and financing activities: | | | | | | | |
| Right-of-use assets acquired under operating leases | 4.9 | 7.1 | | | | | |
| Capital expenditures incurred but not yet paid | 0.6 | 1.3 | 0.2 | 2.7 | 2.0 | 0.8 | 0.5 |