Financial Instruments Financial Instruments (Details Textual 2) - USD ($) shares in Millions, number in Millions, $ in Millions	1 Months Ended	9 Months Ended
	Apr. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Business Acquisition [Line Items]
Proceeds from sales of strategic investments		$ 0.5	$ 476.0
Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio		$ 925.1
Other noncurrent assets | Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio				$ 393.9
Denali Therapeutics
Business Acquisition [Line Items]
Investment in common stock, shares purchased		13
Dividend yield percentage		0.00%
Sangamo
Business Acquisition [Line Items]
Investment in common stock, shares purchased	24
Dividend yield percentage	0.00%