Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Oct. 01, 2016	Jul. 02, 2016	Apr. 02, 2016	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Numerator:
Net income attributable to Weight Watchers International, Inc.									$ 163,514	$ 67,699	$ 32,945
Denominator:
Weighted average shares of common stock outstanding									64,329	63,742	58,369
Effect of dilutive common stock equivalents									3,919	2,155	597
Weighted average diluted common shares outstanding									68,248	65,897	58,966
Earnings Per Share attributable to Weight Watchers International, Inc.
Basic	$ 0.97	$ 0.69	$ 0.70	$ 0.17	$ 0.21	$ 0.54	$ 0.48	$ (0.17)	$ 2.54	$ 1.06	$ 0.56
Diluted	$ 0.91	$ 0.65	$ 0.67	$ 0.16	$ 0.20	$ 0.53	$ 0.46	$ (0.17)	$ 2.40	$ 1.03	$ 0.56