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Summary of Significant Accounting Policies - 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
Accounting Policies [Abstract]          
Accrued performance fee-related compensation $ 1,803.9   $ 1,803.9   $ 1,307.4
Percentage of estimated realizable tax benefit to be paid by corporate taxpayers on exchange transactions     85.00%    
Percentage of remaining estimated realizable tax benefit on exchange transactions     15.00%    
Foreign currency transaction (gain) loss $ 0.7 $ 7.9 $ 2.2 $ 30.8