XML 51 R38.htm IDEA: XBRL DOCUMENT v3.8.0.1
Investments in Marketable Securities - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]          
Investments in marketable securities $ 92.4   $ 92.4   $ 122.4
Proceeds from sale of available-for-sale securities 15.4 $ 12.6 58.7 $ 47.0  
Realized gains on available-for-sale securities 7.4 $ 6.2 19.2 $ 15.4  
Proceeds from sale of trading securities 8.2   23.2    
Realized gains on trading securities $ 1.7   $ 5.0