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