Quarterly Results (Unaudited) - Summary of Historical Revenues Gross Profit Income (Loss) From Operations (Detail) - 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
Revenues:
Gross profit	$ 167,421	$ 176,130	$ 15,739	$ 115,704	$ 293,239	$ 164,932	$ 208,646	$ 172,060
(Loss) income from operations	(112,238)	(27,099)	(126,794)	(611,370)	(227,055)	(277,526)	97,485	(10,297)	$ (877,501)	$ (417,393)	$ 278,285
Net (loss) income	(96,395)	239,665	(130,059)	(541,668)	(268,829)	(281,745)	48,005	(30,289)	(528,457)	(532,858)	122,819
Net (loss) income attributable to common shareholders of Party City Holdco Inc.:	$ (96,417)	$ 239,707	$ (130,015)	$ (541,513)	$ (268,818)	$ (281,533)	$ 48,074	$ (30,218)	$ (528,238)	$ (532,495)	$ 123,259
Net (loss) income per share attributable to common shareholders of Party City Holdco Inc.—Basic	$ (0.88)	$ 2.25	$ (1.39)	$ (5.80)	$ (2.88)	$ (3.02)	$ 0.52	$ (0.32)	$ (5.24)	$ (5.71)	$ 1.28
Net (loss) income per share attributable to common shareholders of Party City Holdco Inc.—Diluted	$ (0.88)	$ 2.24	$ (1.39)	$ (5.80)	$ (2.88)	$ (3.02)	$ 0.51	$ (0.32)	$ (5.24)	$ (5.71)	$ 1.27
Net Sales [Member]
Revenues:
Net sales	$ 645,284	$ 532,053	$ 253,646	$ 412,461	$ 728,361	$ 538,345	$ 561,702	$ 511,102	$ 1,843,444	$ 2,339,510	$ 2,416,442
Royalties and Franchise Fees [Member]
Revenues:
Net sales	$ 2,897	$ 1,722	$ 1,045	$ 1,582	$ 3,190	$ 1,886	$ 2,189	$ 2,014	$ 7,246	$ 9,279	$ 11,073