Silvercrest Asset Management Group LLC Quarterly report pursuant to Section 13 or 15(d)

Investments and Fair Value Measurements - Schedule of Inputs Used in Fair Value Measurement of Estimated Contingent Consideration (Detail) - Level 3 $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity consideration for SLP acquired	$ 14,833	$ 15,921	$ 755
Forecasted Growth Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value measurement input of estimated contingent consideration	16.1	18.6
Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value measurement input of estimated contingent consideration	11.6	10.5