Summary of Significant Accounting Policies (Details 4)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Information
Number of businesses in which the company operates	1
Shares of convertible preferred stock (common stock equivalent)
Net Loss per Common Share
Potentially dilutive securities excluded from the computations of diluted weighted-average shares outstanding because of anti-dilutive effect	8,804,000
Shares underlying outstanding options to purchase common stock
Net Loss per Common Share
Potentially dilutive securities excluded from the computations of diluted weighted-average shares outstanding because of anti-dilutive effect	2,788,599	1,784,285	1,415,106
Shares of unvested restricted stock
Net Loss per Common Share
Potentially dilutive securities excluded from the computations of diluted weighted-average shares outstanding because of anti-dilutive effect		16,000
Shares underlying outstanding warrants to purchase common stock
Net Loss per Common Share
Potentially dilutive securities excluded from the computations of diluted weighted-average shares outstanding because of anti-dilutive effect	14,403,716	200,268	140,520