Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Additional Information (Detail)

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Fair Value Measurements - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Jun. 30, 2014
Minimum [Member]
Jun. 30, 2014
Maximum [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]          
Investments designated as held-to-maturity carrying value $ 14.70        
Sale of investments designated as held-to-maturity 15.5        
Realized gain on sale of investments designated as held-to-maturity 0.8        
Available-for-sale debt securities at fair value 20.7 3.2      
Available-for-sale debt securities at cost 19.6        
Realized gain on sale of investments 1.1        
Discount rates based on market observations       7.00% 15.00%
Discount rates to determine fair market value of underlying assets       8.00% 10.00%
Cash deposits held in U.S. banks 48.2   81.7    
Bank deposits $ 46.8   $ 80.8