Segment Information - General (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Net product sales, cost of product sales and gross profit by product
Number of operating segments | segment									1
Net product sales									$ 1,448.8	$ 1,627.8	$ 1,725.3
Cost of product sales	$ 28.8	$ 33.0	$ 26.7	$ 29.1	$ 31.9	$ 51.9	$ 61.7	$ 53.2	117.6	198.7	105.7
Gross profit									1,331.2	1,429.1	1,619.6
Remodulin
Net product sales, cost of product sales and gross profit by product
Net product sales									587.0	599.0	670.9
Cost of product sales									21.1	14.1	15.9
Gross profit									565.9	584.9	655.0
Tyvaso
Net product sales, cost of product sales and gross profit by product
Net product sales									415.6	415.2	372.9
Cost of product sales									19.6	17.3	18.5
Gross profit									396.0	397.9	354.4
Orenitram
Net product sales, cost of product sales and gross profit by product
Net product sales									225.3	205.1	185.8
Cost of product sales									15.0	13.2	15.3
Gross profit									210.3	191.9	170.5
Unituxin
Net product sales, cost of product sales and gross profit by product
Net product sales									113.7	84.8	76.0
Cost of product sales									15.7	14.3	12.9
Gross profit									98.0	70.5	63.1
Adcirca
Net product sales, cost of product sales and gross profit by product
Net product sales									107.2	323.7	419.7
Cost of product sales									46.2	139.8	43.1
Gross profit									$ 61.0	$ 183.9	$ 376.6