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Investments - Additional Information (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2015
USD ($)
Investment
Dec. 31, 2014
USD ($)
Investments Debt And Equity Securities [Abstract]    
Number of investments in marketable equity securities | Investment 2  
Fair value of marketable equity securities $ 18.1 $ 30.8
Marketable equity securities, unrealized gain (loss) 12.7 $ 18.3
Other- than- temporary impairment $ 1.2