Net Income Per Share of Class A Common Stock - Schedule of Net Income Per Share of Class A Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net Income Attributable to PJT Partners Inc.	$ 46,112	$ 30,907	$ 21,670	$ 18,860	$ 16,810	$ 6,825	$ 4,826	$ 1,101	$ 117,549	$ 29,562	$ 27,170
Dividends on Participating Securities									11	20	128
Net Income Attributable to Participating Securities									$ 41	$ 34	$ 143
Unvested Restricted Stock Units
Denominator:
Weighted-Average Number of Incremental Shares from Unvested RSUs and Partnership Units									18,630,881	1,007,431	2,374,487
Class A Common Stock
Numerator:
Net Income Attributable to Shares of Class A Common Stock — Basic									$ 117,497	$ 29,508	$ 26,899
Incremental Net Income from Dilutive Securities									72,452	879	1,325
Net Income Attributable to Shares of Class A Common Stock — Diluted									$ 189,949	$ 30,387	$ 28,224
Denominator:
Weighted-Average Shares of Class A Common Stock Outstanding — Basic									24,496,285	24,007,138	21,879,574
Weighted-Average Shares of Class A Common Stock Outstanding — Diluted									43,127,166	25,014,569	24,254,061
Net Income Per Share of Class A Common Stock
Basic	$ 1.87	$ 1.25	$ 0.88	$ 0.78	$ 0.71	$ 0.28	$ 0.20	$ 0.05	$ 4.80	$ 1.23	$ 1.23
Diluted	$ 1.67	$ 1.22	$ 0.86	$ 0.72	$ 0.69	$ 0.28	$ 0.20	$ 0.04	$ 4.40	$ 1.21	$ 1.16