Segment Information - General (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Net product sales, cost of product sales and gross profit by product
Number of operating segments | segment			1
Net product sales	$ 362.0	$ 373.6	$ 718.3	$ 736.2
Cost of product sales	25.9	26.7	49.3	55.8
Gross profit	336.1	346.9	669.0	680.4
Remodulin
Net product sales, cost of product sales and gross profit by product
Net product sales	119.0	155.8	264.3	311.3
Cost of product sales	5.3	4.5	11.3	10.6
Gross profit	113.7	151.3	253.0	300.7
Tyvaso
Net product sales, cost of product sales and gross profit by product
Net product sales	119.2	109.6	222.1	213.4
Cost of product sales	4.6	3.5	9.7	7.9
Gross profit	114.6	106.1	212.4	205.5
Orenitram
Net product sales, cost of product sales and gross profit by product
Net product sales	75.4	54.0	144.4	112.4
Cost of product sales	3.9	4.0	8.6	8.8
Gross profit	71.5	50.0	135.8	103.6
Unituxin
Net product sales, cost of product sales and gross profit by product
Net product sales	29.0	25.1	55.6	50.0
Cost of product sales	3.9	2.2	6.2	7.3
Gross profit	25.1	22.9	49.4	42.7
Adcirca
Net product sales, cost of product sales and gross profit by product
Net product sales	19.4	29.1	31.9	49.1
Cost of product sales	8.2	12.5	13.5	21.2
Gross profit	$ 11.2	$ 16.6	$ 18.4	$ 27.9