Cash and Investments in Marketable Securities - Cash and Investments in Marketable Securities, Including Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	$ 55,570	$ 12,365	$ 39,067	$ 25,437
Short-term investments	253,374	225,459
Restricted cash	0	25,000
Total cash and investments in marketable securities	$ 308,944	$ 262,824