Fair Value on Financial Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Fair value of financial assets and liabilities
Total financial assets	$ 10,268		$ 8,970
Total financial liabilities	5,903		7,979
Money Market Funds
Fair value of financial assets and liabilities
Total financial assets	10,268	[1]	8,683	[1]
Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	5,903	[2]	7,979	[2]
United States government agency securities
Fair value of financial assets and liabilities
Total financial assets			287	[3]
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value of financial assets and liabilities
Total financial assets	10,268		8,683
Total financial liabilities	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money Market Funds
Fair value of financial assets and liabilities
Total financial assets	10,268	[1]	8,683	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	0	[2]	0	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets			0	[3]
Significant Other Observable Inputs (Level 2)
Fair value of financial assets and liabilities
Total financial assets	0		287
Total financial liabilities	0		0
Significant Other Observable Inputs (Level 2) | Money Market Funds
Fair value of financial assets and liabilities
Total financial assets	0	[1]	0	[1]
Significant Other Observable Inputs (Level 2) | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	0	[2]	0	[2]
Significant Other Observable Inputs (Level 2) | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets			287	[3]
Significant Unobservable Inputs (Level 3)
Fair value of financial assets and liabilities
Total financial assets	0		0
Total financial liabilities	5,903		7,979
Significant Unobservable Inputs (Level 3) | Money Market Funds
Fair value of financial assets and liabilities
Total financial assets	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	5,903	[2]	7,979	[2]
Significant Unobservable Inputs (Level 3) | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets			$ 0	[3]

[1] Included in cash and cash equivalents on the Company's consolidated balance sheets.

[2] Included in current liabilities on the Company's consolidated balance sheets.

[3] Included in short-term investments on the Company's consolidated balance sheets.