Notes Receivable from Partners - Schedule of Notes Receivable from Partners (Detail) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended	12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Dec. 31, 2019
Accounts Notes And Loans Receivable [Line Items]
Interest accrued and capitalized on notes receivable	$ 2	$ 2	$ 2	$ 3	$ 3	$ 3
Partners
Accounts Notes And Loans Receivable [Line Items]
Beginning balance			$ 645			$ 924	$ 645	$ 924
Repayment of notes							(300)	(291)
Interest accrued and capitalized on notes receivable							5	12
Ending balance	$ 350						$ 350	$ 645