Revenue Recognition - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Adjustments related to prior period sales	$ 8,603
Deferred revenue	6,400
Current portion of deferred revenue	2,112	$ 0
Perosphere Pharmaceuticals Inc.
Disaggregation of Revenue [Line Items]
Potential milestone payment receivable	34,800
Potential milestone payment receivable, subject to FDA clearance	$ 34,800

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