Weighted-Average Assumptions (Detail) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Class of Warrant or Right [Line Items]
Expected dividend yield	0.00%		0.00%
Shares underlying warrants classified as liabilities	2,628,923		3,127,678
Market value of stock at beginning of year	$ 25.80		$ 4.50
Market value of stock at end of period	$ 38.04		$ 25.80
Minimum
Class of Warrant or Right [Line Items]
Risk-free interest rate	0.20%		0.20%
Expected lives	7 months 6 days		1 year 1 month 6 days
Expected volatility	74.00%	[1]	139.20%	[1]
Maximum
Class of Warrant or Right [Line Items]
Risk-free interest rate			0.30%
Expected lives	1 year 2 months 12 days		1 year 7 months 6 days
Expected volatility	91.60%	[1]	164.10%	[1]

[1] For the three and six months ended June 30, 2013, expected volatility has been estimated using a blend of calculated volatility of the Company's common stock over a historical period and implied volatility in exchange-traded options associated with the Company's common stock. Prior to January 1, 2013, expected volatility has been estimated using calculated volatility of the Company's common stock over a historical period commensurate with the expected term of the option.