Weighted-Average Assumptions (Detail) (USD $)	9 Months Ended		12 Months Ended
	Sep. 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	959,283		3,127,618
Market value of stock at beginning of year	$ 25.80		$ 4.50
Market value of stock at end of period	$ 47.23		$ 25.80
Minimum
Class of Warrant or Right [Line Items]
Risk-free interest rate	0.10%		0.20%
Expected lives	9 months 18 days		1 year 1 month 6 days
Expected volatility	67.80%	[1]	139.20%	[1]
Maximum
Class of Warrant or Right [Line Items]
Risk-free interest rate			0.30%
Expected lives	10 months 24 days		1 year 7 months 6 days
Expected volatility	72.70%	[1]	164.10%	[1]

[1] For the three and nine months ended September 30, 2013, expected volatility was 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 was estimated using calculated volatility of the Company's common stock over a historical period commensurate with the expected term of the option.