Stock compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock compensation
Stock compensation expense	$ 40.6	$ 36.6	$ 81.2	$ 72.8
Stock Compensation Expense Capitalized	0.1		$ 0.2
Weighted-average fair value assumptions
Valuation method			Black-Scholes valuation model
Dividend yield (as a percent)			0.00%
Research and Development Expense [Member]
Stock compensation
Stock compensation expense	27.6	24.8	$ 55.0	49.0
Selling, General and Administrative Expenses [Member]
Stock compensation
Stock compensation expense	12.8	$ 11.8	25.8	$ 23.8
Cost of product revenues
Stock compensation
Stock compensation expense	$ 0.2		$ 0.4
Stock Options
Weighted-average fair value assumptions
Average risk-free interest rates (as a percent)	2.26%	2.71%	2.49%	2.47%
Average expected life (in years)	5 years 6 months 18 days	5 years 4 months 13 days	5 years 4 months 2 days	5 years 6 months
Volatility (as a percent)	39.00%	46.00%	45.00%	45.00%
Weighted-average fair value (in dollars per share)	$ 30.92	$ 28.65	$ 31.47	$ 39.47
Unrecognized compensation
Unrecognized compensation cost for nonvested option (in dollars)	$ 110.3		$ 110.3
Vesting period of recognition of the unrecognized compensation cost of nonvested awards			1 year 6 months
Restricted Stock Units (RSUs)
Weighted-average fair value assumptions
Average risk-free interest rates (as a percent)	1.75%	2.52%	2.10%	2.50%
Average expected life (in years)	6 months	6 months	6 months	6 months
Volatility (as a percent)	37.00%	30.00%	34.00%	51.00%
Weighted-average fair value (in dollars per share)	$ 13.11	$ 12.11	$ 13.69	$ 16.25
Unrecognized compensation
Unrecognized compensation cost for nonvested option (in dollars)	$ 49.3		$ 49.3
Vesting period of recognition of the unrecognized compensation cost of nonvested awards			1 year 6 months
Performance Stock Units (PSUs)
Unrecognized compensation
Unrecognized compensation cost for nonvested option (in dollars)	$ 32.7		$ 32.7
Vesting period of recognition of the unrecognized compensation cost of nonvested awards			2 years 7 months 6 days

Represents the amount of stock compensation expenses capitalized.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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Description of method used to estimate fair value of award under share-based payment arrangement.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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