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Investment - Summary of Ranges and Weighted Averages of Significant Unobservable Inputs Used to Quantitative Assessments (Detail) - Advisor Engine [Member] - Preferred Stock [Member] - Level 3 [Member] | 12 Months Ended
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Dec. 31, 2018
Minimum [Member] | Market Approach Valuation Technique [Member] |
Fair Value Inputs Assets Quantitative Informations [Line Items] |
Revenue multiple | 4.7
Maximum [Member] | Market Approach Valuation Technique [Member] |
Fair Value Inputs Assets Quantitative Informations [Line Items] |
Revenue multiple | 5.4
Weighted Average [Member] | Market Approach Valuation Technique [Member] |
Fair Value Inputs Assets Quantitative Informations [Line Items] |
Revenue multiple | 5.0
Weighted Average [Member] | Income Approach Valuation Technique [Member] |
Fair Value Inputs Assets Quantitative Informations [Line Items] |
Weighted average cost of capital ("WACC") | 26.00%

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- Definition Value of input used to measure investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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