Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Numerator:
Net income attributable to Weight Watchers International, Inc.	$ 70,132	$ 44,719	$ 179,964	$ 100,544
Denominator:
Weighted average shares of common stock outstanding	66,701	64,463	66,074	64,237
Effect of dilutive common stock equivalents	3,630	4,223	4,043	3,702
Weighted average diluted common shares outstanding	70,331	68,686	70,117	67,939
Earnings Per Share attributable to Weight Watchers International, Inc.
Basic	$ 1.05	$ 0.69	$ 2.72	$ 1.57
Diluted	$ 1.00	$ 0.65	$ 2.57	$ 1.48