Segment Information - General (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Net product sales, cost of product sales and gross profit by product
Number of operating segments | segment			1
Net product sales	$ 380.1	$ 401.5	$ 1,098.4	$ 1,137.7
Cost of product sales	24.0	33.0	73.3	88.8
Gross profit	356.1	368.5	1,025.1	1,048.9
Remodulin
Net product sales, cost of product sales and gross profit by product
Net product sales	124.5	168.3	388.8	479.6
Cost of product sales	4.9	5.5	16.2	16.1
Gross profit	119.6	162.8	372.6	463.5
Tyvaso
Net product sales, cost of product sales and gross profit by product
Net product sales	129.5	110.8	351.6	324.2
Cost of product sales	5.0	6.9	14.7	14.8
Gross profit	124.5	103.9	336.9	309.4
Orenitram
Net product sales, cost of product sales and gross profit by product
Net product sales	74.7	62.0	219.1	174.4
Cost of product sales	5.1	3.5	13.7	12.3
Gross profit	69.6	58.5	205.4	162.1
Unituxin
Net product sales, cost of product sales and gross profit by product
Net product sales	37.6	30.1	93.2	80.1
Cost of product sales	2.9	4.1	9.1	11.4
Gross profit	34.7	26.0	84.1	68.7
Adcirca
Net product sales, cost of product sales and gross profit by product
Net product sales	13.8	30.3	45.7	79.4
Cost of product sales	6.1	13.0	19.6	34.2
Gross profit	$ 7.7	$ 17.3	$ 26.1	$ 45.2