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Cash and Investments in Marketable Securities - Cash and Investments in Marketable Securities, Including Cash Equivalents (Detail) - USD ($)
$ in Thousands
Jun. 30, 2016
Dec. 31, 2015
Jun. 30, 2015
Dec. 31, 2014
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]        
Cash and cash equivalents $ 55,676 $ 55,570 $ 20,875 $ 12,365
Short-term investments 219,178 253,374    
Total cash and investments in marketable securities $ 274,854 $ 308,944