Income Taxes - Deferred Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carry-forwards	$ 27.7	$ 12.9
Research and other credit carry-forwards	236.7	220.0
Deferred revenue	40.0	37.7
Share-based compensation	24.3	26.1
Cost sharing adjustment	0.0	12.2
Reserves and accruals not currently deductible	55.8	62.7
Operating lease liabilities	48.3	0.0
Other	12.0	13.2
Total deferred tax assets	444.8	384.8
Valuation allowance	(249.4)	(233.7)
Deferred tax assets, net of valuation allowance	195.4	151.1
Deferred tax liabilities:
Property and equipment basis differences	(39.2)	(40.6)
Purchased intangibles	(27.8)	(13.7)
Unremitted foreign earnings	(23.7)	(26.4)
Deferred compensation and other	(8.7)	(8.9)
Operating lease assets	(41.1)	0.0
Total deferred tax liabilities	(140.5)	(89.6)
Net deferred tax assets	54.9	61.5
Valuation allowance	249.4	233.7
Increase (decrease) in DTA valuation allowance	15.7	$ 19.2
Undistributed earnings of foreign subsidiaries	35.8
Additional income tax expense related to undistributed earnings	7.1
Federal
Deferred tax liabilities:
Net operating loss carry-forwards	101.2
Tax credit carry-forwards	4.7
California
Deferred tax liabilities:
Net operating loss carry-forwards	134.0
Tax credit carry-forwards	262.5
California Deferred Tax Assets
Deferred tax assets:
Valuation allowance	(221.6)
Deferred tax liabilities:
Valuation allowance	221.6
Net operating loss carry-forwards	134.0
Massachusetts Deferred Tax Assets
Deferred tax assets:
Valuation allowance	(20.2)
Deferred tax liabilities:
Valuation allowance	20.2
Canadian Deferred Tax Assets
Deferred tax assets:
Valuation allowance	(3.1)
Deferred tax liabilities:
Valuation allowance	3.1
Capital Loss Carryforward
Deferred tax assets:
Valuation allowance	(4.5)
Deferred tax liabilities:
Valuation allowance	$ 4.5