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Financial Instruments and Fair Value Measurement - Additional Information (Detail) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2016
Dec. 31, 2015
Maximum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Liquid investments, original maturities P90D  
Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated fair value of acquisition payable   $ 9,900,000
Discounted cash flows, discount rate   27.50%
Level 3 [Member] | ETP [Member] | Europe [Member] | Minimum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Projected AUM   $ 1,000,000,000
Level 3 [Member] | ETP [Member] | Europe [Member] | Maximum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Projected AUM   6,000,000,000
Fair Value, Inputs, Level 1 [Member] | Other Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments owned $ 125,000 0
Fair Value, Inputs, Level 1 [Member] | Other Liabilities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments sold, but not yet purchased $ 114,000 $ 0