Stockholders Equity - Additional Information (Details) $ in Thousands	1 Months Ended						3 Months Ended						9 Months Ended		60 Months Ended
	Aug. 31, 2018 shares	Mar. 31, 2018 shares	Jul. 31, 2017 shares	Jan. 31, 2017 shares	Nov. 30, 2014 shares	Apr. 30, 2014 shares	Sep. 30, 2020 USD ($) shares	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2019 shares	Dec. 31, 2019 shares
Class Of Stock [Line Items]
Treasury stock, shares							3,683,415						3,683,415			2,757,558
Treasury stock shares acquired (in shares)													925,857	1,046,490
Treasury stock shares acquired | $							$ 952	$ 766	$ 31,636	$ 2,463	$ 12,640	$ 26,970	$ 33,354	$ 42,073
Number of units held by noncontrolling interest holders							11,051,045						11,051,045			12,958,022
Group LP
Class Of Stock [Line Items]
Noncontrolling interests (as a percent)							17.00%						17.00%			21.00%
Class A Common Stock
Class Of Stock [Line Items]
Aggregate stock issuance (in shares)						15,263,653
Common stock, shares issued							59,144,937						59,144,937			52,773,617
Treasury stock, shares							3,683,415						3,683,415			2,757,558
Common stock, shares outstanding							55,461,522						55,461,522			50,016,059
Increase in shares outstanding	4,685,217	4,689,295	5,680,903	5,356,876	4,511,058										24,923,349
Number of shares of common stock to be issued upon exchange of a partnership unit							1						1
Class A Common Stock | Group LP
Class Of Stock [Line Items]
Common stock, shares outstanding							55,461,522						55,461,522			50,016,059
Class B Common Stock
Class Of Stock [Line Items]
Common stock, shares issued							8,490,938						8,490,938			10,397,915
Common stock, shares outstanding							8,490,938						8,490,938			10,397,915
Increase in shares outstanding						36,158,698
Ratio of subscription price to the initial public offering price of shares of common stock					0.00055
Dividends payable ratio to outstanding shares of publicly traded common stock					0.00055