Income Taxes (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 24, 2019	Mar. 31, 2019	Mar. 31, 2018
Effective income tax rate (as a percent)		24.00%	21.00%
Unrecognized tax benefits		$ 0.5	$ 0.5
Positions of unrecognized tax benefits, if realized, would impact the effective tax rate		0.3	$ 0.3
Arena Pharmaceuticals, Inc.
One-time payment	$ 800.0
Increase in deferred tax assets		$ 169.8