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Fair Value Measurements - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Sep. 30, 2015
Jun. 30, 2016
Dec. 31, 2015
Jun. 30, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Estimated fair value of long-term debt   $ 2,190.0 $ 2,150.0 $ 2,140.0
Long-term debt   $ 2,100.0 $ 2,100.0 $ 2,100.0
Auction Rate Securities        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Proceeds from sale of debt security $ 32.3