Summary of Significant Accounting Policies - Schedule of Reconciliation Between Basic and Diluted Income Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share Basic And Diluted [Line Items]
Net (loss) income attributable to common shareholders of Party City Holdco Inc.	$ (268,818)	$ (281,533)	$ 48,074	$ (30,218)	$ 98,325	$ (2,420)	$ 28,487	$ (1,133)	$ (532,495)	$ 123,259	$ 215,340
Weighted average shares - Basic									93,295,692	96,133,144	118,589,421
Effect of dilutive restricted stock units:									0	1,128,245	1,304,600
Weighted average shares - Diluted									93,295,692	97,271,050	119,894,021
Net (loss) income per share attributable to common shareholders of Party City Holdco Inc. - Basic	$ (2.88)	$ (3.02)	$ 0.52	$ (0.32)	$ 1.03	$ (0.03)	$ 0.30	$ (0.01)	$ (5.71)	$ 1.28	$ 1.81
Net (loss) income per share attributable to common shareholders of Party City Holdco Inc. - Diluted	$ (2.88)	$ (3.02)	$ 0.51	$ (0.32)	$ 1.02	$ (0.03)	$ 0.29	$ (0.01)	$ (5.71)	$ 1.27	$ 1.79
Restricted Stock Units (RSUs) [Member]
Earnings Per Share Basic And Diluted [Line Items]
Effect of dilutive restricted stock units:									0	9,661	0