Investments - Summary Of Equity Investments were Valued Using a Market Approach (Detail)	Sep. 30, 2020
Measurement Input Discount For Lack Of Control [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Securities, Measurement Input	13
Measurement Input, Discount for Lack of Marketability [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Securities, Measurement Input	30
Measurement Input, Discount for Lack of Marketability [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Securities, Measurement Input	10