| In millions, except per share items | Apr-30-15 | Apr-30-14 | Apr-30-13 | Apr-30-12 | Apr-30-11 | Apr-30-10 | Apr-30-09 | Apr-30-08 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Cash flows from operating activities: | | | | | | | | |
| Net income | 93.4 | 95.0 | 42.9 | 65.8 | 124.5 | | | |
| Adjustments to reconcile net income to net cash from operating activities: | | | | | | | | |
| Depreciation and amortization | 34.7 | 32.7 | 32.5 | 29.8 | 20.6 | 22.7 | | |
| Change in fair value of interest rate swap | -0.9 | -1.2 | -0.6 | 0.9 | 0.2 | -0.8 | | |
| Stock-based compensation | 34.1 | 35.0 | 33.5 | 27.3 | 19.8 | 23.5 | | |
| Tax effect from stock-based compensation | 2.6 | 3.0 | 3.7 | 0.9 | 0.6 | | | |
| (Gain) loss on equity investments, net | -12.6 | -21.4 | -20.0 | -10.4 | -13.2 | -7.0 | | |
| Write-down of inventories | 41.2 | 33.2 | 23.1 | 17.1 | 18.3 | 19.2 | | |
| Excess tax benefit from stock-based compensation | -2.0 | -2.5 | -2.7 | -0.5 | -0.1 | | | |
| Gain on disposal of property, plant and equipment | 0.0 | -0.2 | 0.2 | 0.0 | 0.0 | 0.1 | | |
| Changes in assets and liabilities: | | | | | | | | |
| Accounts receivable, net | 21.4 | -6.0 | -58.7 | 34.8 | -68.4 | -30.3 | | |
| Inventories | -111.6 | 128.8 | -163.5 | -204.6 | 5.6 | -45.2 | | |
| Prepaid and deferred income taxes | -5.8 | 8.3 | -4.4 | | 5.6 | -2.7 | | |
| Prepaid expenses and other assets | 13.5 | 2.8 | 10.2 | 2.1 | 3.2 | -0.3 | | |
| Accounts payable | -21.7 | -47.2 | 29.9 | 58.2 | 18.7 | 51.9 | | |
| Accrued expenses and other liabilities | 9.0 | -1.1 | 5.3 | -2.4 | -0.2 | 2.4 | | |
| Income taxes payable | -17.0 | -4.9 | 3.2 | 1.6 | -2.7 | 7.4 | | |
| Deferred revenues, less cost of revenues | -3.0 | 10.5 | 4.8 | -6.5 | 5.9 | 3.5 | | |
| Net cash provided by operating activities | 75.2 | 237.9 | -60.6 | 8.4 | 137.3 | 48.3 | | |
| |
| Cash flows from investing activities: | | | | | | | | |
| Purchases of short-term investments | -356.5 | -228.2 | -309.3 | -187.3 | -161.9 | -135.0 | -59.2 | -78.0 |
| Proceeds from sales or maturities of short-term investments | 301.7 | 102.4 | 327.2 | 230.9 | 170.2 | 52.1 | | |
| Purchases of property, plant and equipment, net of sales | -11.3 | -14.8 | -35.3 | -24.2 | -10.3 | -13.5 | | |
| Purchase and deposits for intangible and other assets | | -12.3 | -20.6 | -6.5 | -63.5 | | | |
| Net cash used in investing activities | -65.8 | -138.0 | -47.1 | -13.0 | -64.7 | -101.5 | | |
| |
| Cash flows from financing activities: | | | | | | | | |
| Repayment of long-term borrowings | -3.8 | -3.8 | -3.1 | -4.3 | -4.3 | -3.6 | | |
| Excess tax benefits from stock-based compensation | 2.0 | 2.5 | 2.7 | 0.5 | 0.1 | | | |
| Proceeds from exercise of stock options and employee stock purchase plan | 13.4 | 13.7 | 7.8 | 19.6 | 76.2 | 15.9 | | |
| Net cash provided by financing activities | 11.6 | 7.9 | 7.4 | -84.3 | 72.0 | 29.3 | | |
| |
| Effect of exchange rate changes on cash and cash equivalents | 0.0 | 0.0 | 0.0 | 0.0 | 0.8 | 0.1 | | |
| Net increase in cash and cash equivalents | 20.9 | 107.8 | -100.3 | -88.9 | 145.4 | -23.8 | | |
| Cash and cash equivalents at beginning of period | 298.0 | 190.2 | 290.5 | 379.4 | 234.0 | 257.8 | | |
| Cash and cash equivalents at end of period | 318.9 | 298.0 | 190.2 | 290.5 | 379.4 | 234.0 | | |
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| Supplemental cash flow information: | | | | | | | | |
| Taxes paid | 8.7 | 3.4 | 4.6 | 1.9 | 1.4 | 3.3 | | |
| Interest paid | 2.1 | 2.4 | 2.6 | 2.7 | 2.8 | 2.1 | | |
| Supplemental schedule of non-cash investing and financing activities: | | | | | | | | |
| Additions to property, plant and equipment included in accounts payable and accrued expenses and other current liabilities | 2.7 | 3.9 | 2.5 | 2.4 | 2.6 | 4.7 | | |
| Write-off of employee stock-based compensation-related deferred tax assets | 1.0 | 0.7 | 1.6 | 2.3 | | | | |