Fair Values on Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair value of financial assets and liabilities
Total financial assets	$ 75,446	$ 96,163
Money market funds
Fair value of financial assets and liabilities
Total financial assets	2,122	59,302
Level 1
Fair value of financial assets and liabilities
Total financial assets	7,052	70,465
Level 1 | Money market funds
Fair value of financial assets and liabilities
Total financial assets	2,122	59,302
Level 2
Fair value of financial assets and liabilities
Total financial assets	68,394	25,698
United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	25,194
United States government agency securities | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	4,998
United States government agency securities | Short-term Investments
Fair value of financial assets and liabilities
Total financial assets	20,196
United States government agency securities | Level 2 | United States government agency securities
Fair value of financial assets and liabilities
Total financial assets	4,998
United States government agency securities | Level 2 | Short-term Investments
Fair value of financial assets and liabilities
Total financial assets	20,196
Corporate debt securities
Fair value of financial assets and liabilities
Total financial assets	43,200	25,698
Corporate debt securities | Level 2
Fair value of financial assets and liabilities
Total financial assets	43,200	25,698
Marketable equity securities
Fair value of financial assets and liabilities
Total financial assets	4,930	11,163
Marketable equity securities | Level 1
Fair value of financial assets and liabilities
Total financial assets	$ 4,930	$ 11,163