Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Oct. 01, 2016	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Disclosure Basis Of Presentation Details [Line Items]
Income before income taxes				$ 145,080	$ 84,127	$ 55,614
Net income attributable to Weight Watchers International, Inc.				163,514	67,699	32,945
(Benefit from) provision for income taxes	$ (56,560)			$ (18,237)	16,634	22,835
Adjustments
Disclosure Basis Of Presentation Details [Line Items]
Income before income taxes					347	1,650
Net income attributable to Weight Watchers International, Inc.		$ 1,576	$ (2,684)		1,791	320
(Benefit from) provision for income taxes		$ (110)	$ 2,684		$ 2,138	$ 1,970