Share-Based Compensation (Share-based Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 3,705	$ 3,402
Research and development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,302	1,047
General and administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	2,403	2,355
Stock Option [Member] | Research and development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,261	558
Stock Option [Member] | General and administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,710	589
Restricted Stock [Member] | Research and development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	30	478
Restricted Stock [Member] | General and administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	619	1,579
Warrant [Member] | Research and development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	11	11
Warrant [Member] | General and administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 74	$ 187