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Quarterly Financial Information - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	Nov. 29, 2017	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
Quarterly Financial Information [Line Items]
Impairment charge										$ 13,323	$ 0	$ 0
Diluted		$ 0.91	$ 0.65	$ 0.67	$ 0.16	$ 0.20	$ 0.53	$ 0.46	$ (0.17)	$ 2.40	$ 1.03	$ 0.56
Write off of deferred financing costs in connection with debt refinancing	$ 4,808	$ 10,524								$ 4,808		$ 647
Income tax (benefit) related to 2017 Tax Act		(56,560)
Income tax (benefit) from closure of Spainish subsidary					$ (11,633)					(11,633)
Reversal of tax reserves from updated transfer pricing study			$ 2,255							2,255
Tax benefit due to change in estimate related to availability of foreign tax credits		3,735								3,735
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
Operating income		$ 49,488	$ 91,378	$ 96,206	$ 30,233	$ 46,730	$ 66,792	$ 73,731	$ 13,557	267,305	200,811	168,058
2017 Tax Act
Quarterly Financial Information [Line Items]
Diluted		$ 0.82
Disposition of Spanish subsidiary
Quarterly Financial Information [Line Items]
Diluted					$ 0.17
Reversal of tax reserves
Quarterly Financial Information [Line Items]
Diluted			$ 0.03
Foreign tax credits
Quarterly Financial Information [Line Items]
Diluted		0.05
Research and development tax credit and Section 199 deduction for the tax years 2012 through 2015
Quarterly Financial Information [Line Items]
Diluted							$ 0.17
(Benefit from) provision for income taxes							$ (11,438)
Debt refinancing
Quarterly Financial Information [Line Items]
Diluted		$ 0.09
Adjustments
Quarterly Financial Information [Line Items]
Diluted						$ 0.02	$ (0.04)
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
Operating income						$ 1,466
BRAZIL
Quarterly Financial Information [Line Items]
Impairment charge		$ 13,323								$ 13,323	$ 0
Diluted		$ 0.19