Fair Values on Financial Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Fair value of financial assets and liabilities
Total financial assets	$ 33,426		$ 36,841
Total financial liabilities	10,485		20,390
Money market funds
Fair value of financial assets and liabilities
Total financial assets	3,912	[1]	8,650	[1]
Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	26,088	[2]	23,173	[3]
United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	3,426	[2]	5,018	[3]
Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	10,485	[4]	20,390	[4]
Level 1
Fair value of financial assets and liabilities
Total financial assets	3,912		8,650
Total financial liabilities	0		0
Level 1 | Money market funds
Fair value of financial assets and liabilities
Total financial assets	3,912	[1]	8,650	[1]
Level 1 | Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	0	[2]	0	[3]
Level 1 | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	0	[2]	0	[3]
Level 1 | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	0	[4]	0	[4]
Level 2
Fair value of financial assets and liabilities
Total financial assets	29,514		28,191
Total financial liabilities	0		0
Level 2 | Money market funds
Fair value of financial assets and liabilities
Total financial assets	0	[1]	0	[1]
Level 2 | Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	26,088	[2]	23,173	[3]
Level 2 | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	3,426	[2]	5,018	[3]
Level 2 | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	0	[4]	0	[4]
Level 3
Fair value of financial assets and liabilities
Total financial assets	0		0
Total financial liabilities	10,485		20,390
Level 3 | Money market funds
Fair value of financial assets and liabilities
Total financial assets	0	[1]	0	[1]
Level 3 | Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	0	[2]	0	[3]
Level 3 | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	0	[2]	0	[3]
Level 3 | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	$ 10,485	[4]	$ 20,390	[4]

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

[2] Included in short-term investments on the Company's consolidated balance sheets, except for approximately $1.0 million of corporate debt securities that are included in cash and cash equivalents on the Company's consolidated balance sheets.

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

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