Fair Value on Financial Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Fair value of financial assets and liabilities
Total financial assets	$ 31,416		$ 36,841
Total financial liabilities	3,931		20,390
Money market funds
Fair value of financial assets and liabilities
Total financial assets	6,185	[1]	8,650	[1]
Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	21,802	[2]	23,173	[2]
United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	3,429	[2]	5,018	[2]
Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	3,931	[3]	20,390	[3]
Level 1
Fair value of financial assets and liabilities
Total financial assets	6,185		8,650
Total financial liabilities	0		0
Level 1 | Money market funds
Fair value of financial assets and liabilities
Total financial assets	6,185	[1]	8,650	[1]
Level 1 | Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	0	[2]	0	[2]
Level 1 | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	0	[2]	0	[2]
Level 1 | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	0	[3]	0	[3]
Level 2
Fair value of financial assets and liabilities
Total financial assets	25,231		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	21,802	[2]	23,173	[2]
Level 2 | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	3,429	[2]	5,018	[2]
Level 2 | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	0	[3]	0	[3]
Level 3
Fair value of financial assets and liabilities
Total financial assets	0		0
Total financial liabilities	3,931		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	[2]
Level 3 | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	0	[2]	0	[2]
Level 3 | Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities	$ 3,931	[3]	$ 20,390	[3]

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

[2] Included in short-term investments on the Company's accompanying unaudited condensed consolidated balance sheets.

[3] Included in current liabilities on the Company's accompanying unaudited condensed consolidated balance sheets.