Weighted-Average Assumptions (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Class of Warrant or Right [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Shares underlying warrants classified as liabilities	791,508	3,127,618	4,824,827
Market value of stock at beginning of year	$ 25.80	$ 4.50	$ 12.72
Market value of stock at end of period	$ 20.37	$ 25.80	$ 4.50
Minimum
Class of Warrant or Right [Line Items]
Risk-free interest rate	0.10%	0.20%	0.10%
Expected lives	7 months 6 days	1 year 1 month 6 days	1 year
Expected volatility	95.51%	139.20%	71.80%
Maximum
Class of Warrant or Right [Line Items]
Risk-free interest rate		0.30%	0.40%
Expected lives	8 months 12 days	1 year 7 months 6 days	2 years 8 months 12 days
Expected volatility		164.10%	75.60%