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, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity consideration for SLP acquired	$ 17,228	$ 19,928	$ 18,588	$ 16,402	$ 15,921
Forecasted Growth Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value measurement input of estimated contingent consideration	16.6			16.4
Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value measurement input of estimated contingent consideration	10.1			11.7