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Intangible Assets and Goodwill - Additional Information (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]        
Pretax impairment charge recorded during the period for intangible assets related to our credit hedge funds     $ 0 $ 0
Intangible asset amortization expense, excluding impairment losses $ 2,600,000 $ 11,100,000 $ 7,600,000 $ 30,400,000