Earnings Per Share - Computation of Basic and Diluted Earnings (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2021	Jun. 27, 2020	Jul. 03, 2021	Jun. 27, 2020
Numerator:
Net income (loss) attributable to WW International, Inc.	$ 8,860	$ 14,006	$ (9,367)	$ 7,943
Denominator:
Weighted average shares of common stock outstanding	69,588	67,641	69,336	67,538
Effect of dilutive common stock equivalents	1,572	2,158		2,360
Weighted average diluted common shares outstanding	71,160	69,799	69,336	69,898
Earnings (loss) per share attributable to WW International, Inc.
Basic	$ 0.13	$ 0.21	$ (0.14)	$ 0.12
Diluted	$ 0.12	$ 0.20	$ (0.14)	$ 0.11