Income Taxes (Details) - USD ($) $ in Millions		1 Months Ended	9 Months Ended
Jan. 24, 2019	Jan. 31, 2019	Sep. 30, 2019	Sep. 30, 2018
Effective income tax rate (as a percent)			33.00%	21.00%
Unrecognized tax benefits			$ 0.9	$ 0.9
Positions of unrecognized tax benefits, if realized, would impact the effective tax rate			0.7	$ 0.7
Arena Pharmaceuticals, Inc.
One-time payment	$ 800.0	$ 800.0
Increase in deferred tax assets			$ 172.4

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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