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Investments - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]      
Proceeds from sales of short term investments $ 505,966 $ 363,110 $ 338,970
Restricted investments $ 15,336 $ 15,485