Summary of Short-term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Investments in mutual funds at fair value	$ 15,016	$ 126,479	$ 186,842
Term deposits with banks	6,598	413,566	$ 466,625
Total	$ 21,614	$ 540,045