Summary of Significant Accounting Policies - Securities Excluded from Calculation of Weighted-Average Shares Outstanding (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Shares of Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of weighted-average shares outstanding		1,792,320		1,792,320
Shares Underlying Options Outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of weighted-average shares outstanding	744,007	563,390	744,007	563,390
Shares Underlying Warrants Outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of weighted-average shares outstanding	6,108,050	5,329,222	6,108,050	5,329,222