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Investment, Carried at Cost - Additional Information (Detail)
12 Months Ended
Dec. 31, 2016
USD ($)
shares
Schedule of Cost-method Investments [Line Items]  
Cost method investments $ 20,000,000
Advisor Engine Inc. [Member]  
Schedule of Cost-method Investments [Line Items]  
Date of agreement Nov. 18, 2016
Cost method investments $ 20,000,000
Ownership interest percentage 36.00%
Impairment losses $ 0
Advisor Engine Inc. [Member] | Series A Preferred [Member]  
Schedule of Cost-method Investments [Line Items]  
Number of shares purchased | shares 11,811,856
Advisor Engine Inc. [Member] | Series A Preferred [Member]  
Schedule of Cost-method Investments [Line Items]  
Non-cumulative dividend 6.00%