Restructuring Activities - Severance Costs (Details) - Accrued Severance and Other Employee Costs - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Cost and Reserve [Line Items]
Severance, stock compensation and other employee costs	$ 0	$ 1,756	$ 0	$ 10,532
Restructuring Reserve [Roll Forward]
Beginning Balance			2,529
Accrued restructuring expenses			0
Payments			(2,082)
Ending Balance	447		447
Research and development
Restructuring Cost and Reserve [Line Items]
Severance, stock compensation and other employee costs	0	1,048	0	5,873
General and administrative
Restructuring Cost and Reserve [Line Items]
Severance, stock compensation and other employee costs	$ 0	$ 708	$ 0	$ 4,649