Goodwill - Schedule of Changes in Goodwill by Reporting Segment (Detail) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Goodwill By Segment [Line Items]
Beginning balance		$ 1,072,330,000			$ 1,072,330,000
Goodwill impairment	$ 0	(401,436,000)	$ (556,056,000)	$ (556,056,000)
Ending balance	661,251,000		1,072,330,000		661,251,000	$ 1,072,330,000
Wholesale Segment [Member]
Schedule Of Goodwill By Segment [Line Items]
Beginning balance		493,432,000			493,432,000	510,490,000
Allocation of Goodwill from/to Retail segment						42,230,000
Goodwill impairment					(148,326,000)	(60,427,000)
Foreign currency translation					1,483,000	1,139,000
Goodwill reclassified to held for sale					(13,405,000)
Ending balance	333,184,000		493,432,000		333,184,000	493,432,000
Retail Segment [Member]
Schedule Of Goodwill By Segment [Line Items]
Beginning balance		$ 578,898,000			578,898,000	1,146,460,000
Sale of Canadian-based Party City stores						(48,241,000)
Allocation of Goodwill from/to Retail segment						(42,230,000)
Goodwill impairment					(253,110,000)	(495,629,000)
Foreign currency translation					767,000	606,000
Ending balance	$ 328,067,000		$ 578,898,000		328,067,000	578,898,000
Retail Segment [Member] | Store Acquisitions [Member]
Schedule Of Goodwill By Segment [Line Items]
Business acquisition					$ 1,512,000	2,557,000
Retail Segment [Member] | Acquisitions [Member]
Schedule Of Goodwill By Segment [Line Items]
Business acquisition						$ 15,375,000