Stock Option Plans, Allocation of Recognized Period Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
All stock-based compensation expense [Abstract]
Total stock-based compensation expense	$ 973	$ 710	$ 2,903	$ 6,303
Research and Development [Member]
All stock-based compensation expense [Abstract]
Total stock-based compensation expense	326	237	822	2,022
General and Administrative [Member]
All stock-based compensation expense [Abstract]
Total stock-based compensation expense	$ 647	$ 473	$ 2,081	$ 4,281