Commitments and Contingencies (Narrative) (Details)	1 Months Ended	12 Months Ended
	May 31, 2016 USD ($) ft²	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2015 USD ($)
Rent expense		$ 7,000,000	$ 4,200,000	$ 3,600,000
Accrued milestone payment associated with the first Phase 3 clinical trial					$ 3,000,000
Notice period required for termination of license agreement		90 days
Aggregate amount of payments made under license agreement		$ 7,600,000
Gaithersburg, Maryland [Member]
Tenant Improvement Allowance	$ 9,600,000	0
Rental Square Footage of Building | ft²	150,000
Facility Lease Term	2030
Rockville, Maryland [Member]
Facility Lease Term	2020
Uppsala, Sweden [Member]
Facility Lease Term	2026
Maximum [Member]
Increase In License Maintenance Fees		300,000
Increase In Milestone Payment		15,000,000
Minimum [Member]
Increase In License Maintenance Fees		200,000
Increase In Milestone Payment		$ 14,000,000