Revision of Prior Years' Financial Statements (Effects of the Error Correction on the Consolidated Statements of Operations) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Research and development	$ 5,506	$ 6,276	$ 19,277	$ 21,336
Total expenses	6,606	7,553	22,924	25,095
Net loss	$ (6,605)	$ (7,551)	$ (22,921)	$ (25,088)
Loss per share - basic and diluted	$ (0.27)	$ (0.32)	$ (0.94)	$ (1.08)
As Previously Reported [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Research and development		$ 6,107		$ 20,882
Total expenses		7,384		24,641
Net loss		$ (7,382)		$ (24,634)
Loss per share - basic and diluted		$ (0.32)		$ (1.06)
Correction [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Research and development		$ 169		$ 454
Total expenses		169		454
Net loss		$ (169)		$ (454)
Loss per share - basic and diluted		$ (0.00)		$ (0.02)