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Financial Instruments Financial Instruments (Details Textual 2) - USD ($) shares in Millions, $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 05, 2018 | Dec. 31, 2017
Strategic Investments |  |  |
Business Acquisition [Line Items] |  |  |
Strategic investment portfolio | $ 549.0 |  | $ 85.8
Ionis Pharmaceuticals |  |  |
Business Acquisition [Line Items] |  |  |
Term of collaboration agreement | 10 years |  |
Total payment to enter collaboration agreement |  | $ 1,000.0 |
Upfront payment for collaboration agreement |  | $ 375.0 |
Investment in common stock, shares purchased |  | 11.5 |
Purchase of common stock |  | $ 625.0 |

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