XML 26 R31.htm IDEA: XBRL DOCUMENT v3.2.0.727
Short Term Investments - Additional Information (Detail) - US Treasury Securities - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2015
Dec. 31, 2014
Investment [Line Items]    
Held to maturity securities, amortized cost $ 226.7 $ 198.5
Held to maturity securities, carrying value 226.7 198.5
Held to maturity securities, fair value 226.7 198.5
Other-than-temporary impairments related to these investments $ 0.0 $ 0.0
Minimum    
Investment [Line Items]    
Held to maturity securities maturity range 3 months  
Maximum    
Investment [Line Items]    
Held to maturity securities maturity range 1 year