Share-Based Payment Arrangements, Allocation of Recognized Period Costs (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expense recognized	$ 3,523	$ 3,546	$ 6,536
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expense recognized	1,843	2,012	4,060
General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expense recognized	$ 1,680	$ 1,534	$ 2,476