Cash and Investments in Marketable Securities - Cash and Investments in Marketable Securities, Including Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	$ 59,640	$ 55,570	$ 12,365	$ 39,067
Short-term investments	329,462	253,374
Total cash and investments in marketable securities	$ 389,102	$ 308,944