Stockholders' Equity (Details 6) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-based compensation expense
Stock-based compensation expense	$ 2,013,000	$ 1,440,000	$ 821,000
Unrecognized compensation expense	3,400,000
Weighted-average period	2 years 6 months
General and Administrative Expense [Member]
Stock-based compensation expense
Stock-based compensation expense	1,026,000	731,000	423,000
Research and Development Expense [Member]
Stock-based compensation expense
Stock-based compensation expense	$ 987,000	$ 709,000	$ 398,000