Subsequent Events (Details)		1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 16, 2019 USD ($)	Feb. 28, 2019 employee	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Subsequent Event [Line Items]
Payment for debt extinguishment				$ 28,054,000	$ 625,000	$ 0
Restructuring charges				$ 0	$ 0	$ 341,000
Subsequent Event
Subsequent Event [Line Items]
Number of positions eliminated | employee		110
Subsequent Event | Perosphere Pharmaceuticals Inc.
Subsequent Event [Line Items]
Upfront purchase price	$ 50,000,000
Cash consideration	40,000,000
Other liabilities	6,200,000
Additional merger consideration	365,000,000
Subsequent Event | Perosphere Convertible Note | Convertible Debt
Subsequent Event [Line Items]
Principal amount of debt at time of issuance	10,000,000.0
Subsequent Event | Perosphere Convertible Note | Convertible Debt | Perosphere Pharmaceuticals Inc.
Subsequent Event [Line Items]
Cancellation of convertible note	10,000,000
Subsequent Event | Perosphere Term Loan | Line of Credit | Perosphere Pharmaceuticals Inc.
Subsequent Event [Line Items]
Payment for debt extinguishment	12,000,000
Subsequent Event | Regulatory Milestone Achievement | Perosphere Pharmaceuticals Inc.
Subsequent Event [Line Items]
Additional merger consideration	$ 140,000,000
Credited percentage	50.00%
Subsequent Event | Milestone Achievement, Approval By European Medicines Agency | Perosphere Pharmaceuticals Inc.
Subsequent Event [Line Items]
Additional merger consideration	$ 40,000,000
Subsequent Event | Sales Milestones Achievement | Perosphere Pharmaceuticals Inc.
Subsequent Event [Line Items]
Additional merger consideration	225,000,000
Subsequent Event | First Sales Milestone Achievement | Perosphere Pharmaceuticals Inc.
Subsequent Event [Line Items]
Contingent consideration, milestone payment	20,000,000
Triggering event, threshold amount (at least)	$ 100,000,000
Scenario, Forecast
Subsequent Event [Line Items]
Restructuring charges			$ 6,000,000