Investments - Investments in Variable Interest Entities (Parenthetical) (Detail) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Receivables from related parties	$ 14,246,000	$ 14,273,000
Maximum exposure to loss	3,700,000	2,800,000
Aqua [Member]
Variable Interest Entity [Line Items]
Receivables from related parties	980,000.0
Subordinated Loan [Member] | Aqua [Member]
Variable Interest Entity [Line Items]
Receivables from related parties	980,000	980,000
Maximum exposure to loss	$ 980,000	$ 980,000