| In millions, except per share items | Dec-31-20 | Sep-30-20 | Jun-30-20 | Mar-31-20 | Dec-31-19 | Sep-30-19 | Jun-30-19 | Mar-31-19 |
| | 10-K | 10-Q | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q |
| CASH FLOWS FROM OPERATING ACTIVITIES: | | | | | | | | |
| Net income | 90.4 | 68.8 | 59.6 | 41.5 | 32.8 | 29.1 | 22.2 | 21.0 |
| Adjustments to reconcile net income to net cash from operating activities: | | | | | | | | |
| Depreciation | 11.1 | 11.4 | 11.5 | 12.0 | 12.6 | 12.8 | 13.3 | 13.6 |
| Stock-based compensation | 33.7 | 35.7 | 36.3 | 36.5 | 35.2 | 33.4 | 32.5 | 31.1 |
| Deferred income taxes | 2.7 | -5.0 | -9.2 | -12.0 | -13.1 | 3.6 | 8.5 | 4.9 |
| Non-cash lease expense | 4.6 | 4.5 | 4.5 | 5.0 | 4.9 | 3.7 | 2.4 | 1.1 |
| Other non-cash charges (benefits) | 0.8 | -0.5 | -1.3 | -1.8 | -2.2 | -2.4 | -2.2 | -1.5 |
| Changes in operating assets and liabilities: | | | | | | | | |
| Accounts receivable | -20.5 | -37.5 | -25.6 | -13.4 | -7.1 | -18.3 | -33.1 | -8.6 |
| Inventory | 2.8 | 2.1 | 6.1 | -9.6 | -15.3 | -2.6 | 12.1 | 30.4 |
| Prepaid expenses and other current assets | -1.5 | -0.4 | -0.9 | 3.6 | 6.1 | 1.9 | 14.0 | 7.7 |
| Other assets | 0.0 | -0.2 | 0.2 | 0.1 | -0.3 | 0.3 | 0.3 | 0.8 |
| Accounts payable | 15.3 | 19.9 | 6.7 | -5.3 | -0.8 | 14.2 | 18.4 | 15.1 |
| Accrued liabilities | -0.2 | 4.2 | 6.6 | 18.3 | 26.8 | 24.8 | 18.8 | -6.3 |
| Deferred revenue | -2.2 | -7.8 | -2.4 | -3.6 | -0.9 | 9.4 | 4.6 | 5.5 |
| Income taxes payable | | | -0.8 | | | | -12.1 | -11.3 |
| Lease liabilities | -5.2 | -5.0 | -5.5 | -5.6 | -4.5 | -3.7 | -1.7 | -0.8 |
| Other long-term liabilities | 0.1 | 0.4 | 0.5 | 0.7 | 0.6 | 1.6 | 1.3 | 0.6 |
| Net cash provided by operating activities | 131.1 | 89.7 | 86.2 | 65.5 | 72.8 | 95.7 | 99.3 | 103.4 |
| |
| CASH FLOWS FROM INVESTING ACTIVITIES: | | | | | | | | |
| Purchases of property and equipment | -12.9 | -13.2 | -12.0 | -11.9 | -11.8 | -12.5 | -11.0 | -10.7 |
| Purchases of marketable securities | -418.9 | -334.4 | | -452.9 | -476.2 | -492.3 | -469.5 | -414.1 |
| Sales and maturities of marketable securities | 383.7 | 401.6 | 450.1 | 405.9 | 384.5 | 423.3 | 358.9 | 343.4 |
| Deposits | | | | | | | | |
| Net cash used in investing activities | -48.2 | 54.0 | 109.7 | -58.9 | -103.6 | -81.6 | -121.7 | -81.5 |
| |
| CASH FLOWS FROM FINANCING ACTIVITIES: | | | | | | | | |
| Proceeds from the issuance of common stock under stock-based compensation plans | 2.2 | 3.1 | 3.5 | 5.9 | 6.9 | 7.0 | 6.9 | 6.2 |
| Net cash provided by (used in) financing activities | 2.2 | 3.1 | 3.5 | 5.9 | 6.9 | -20.0 | -32.1 | -33.5 |
| |
| Supplemental cash flow disclosures: | | | | | | | | |
| Cash paid (refunds received) for income taxes, net | 3.1 | 2.2 | 1.5 | -1.6 | -0.1 | 0.8 | -6.7 | -4.1 |
| Supplemental disclosure of non-cash investing and financing activities: | | | | | | | | |
| Capital expenditures incurred but not yet paid | 0.6 | 1.0 | 0.6 | 1.3 | 1.3 | -0.9 | 0.8 | -0.5 |