Fair Values on Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair value of financial assets and liabilities
Total financial assets	$ 96,163	$ 33,426
Total financial liabilities		10,485
Money market funds
Fair value of financial assets and liabilities
Total financial assets	59,302	3,912
Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	25,698	26,088
United States government agency securities
Fair value of financial assets and liabilities
Total financial assets		3,426
Marketable equity securities
Fair value of financial assets and liabilities
Total financial assets	11,163
2010 Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities		10,485
Level 1
Fair value of financial assets and liabilities
Total financial assets	70,465	3,912
Level 1 | Money market funds
Fair value of financial assets and liabilities
Total financial assets	59,302	3,912
Level 1 | Marketable equity securities
Fair value of financial assets and liabilities
Total financial assets	11,163
Level 2
Fair value of financial assets and liabilities
Total financial assets	25,698	29,514
Level 2 | Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	$ 25,698	26,088
Level 2 | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets		3,426
Level 3
Fair value of financial assets and liabilities
Total financial liabilities		10,485
Level 3 | 2010 Warrant Liability
Fair value of financial assets and liabilities
Total financial liabilities		$ 10,485