Restructuring Expenses (Details) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Feb. 28, 2017 position	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Restructuring Reserve [Roll Forward]
Restructuring expense		$ 387	$ 337	$ 3,523	$ 9,999	$ 224	$ 8	$ 343	$ 687	$ 14,246	$ 1,262	$ 2,206
Research and development restructuring
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | position	70
Restructuring Reserve [Roll Forward]
Liability, beginning of the period					$ 0					0
Restructuring expense										12,503
Cash payments										(8,602)
Asset impairments and other non-cash items										(1,812)
Liability, end of the period		$ 2,089				$ 0				$ 2,089	$ 0