Information About Reportable Segments (Detail) - USD ($) $ 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
Segment Reporting Information [Line Items]
Net revenue		$ 312,488	$ 323,687	$ 341,673	$ 329,063	$ 267,412	$ 280,819	$ 309,761	$ 306,910	$ 1,306,911	$ 1,164,902	$ 1,164,419
Operating income		49,488	91,378	96,206	30,233	46,730	66,792	73,731	13,557	267,305	200,811	168,058
Interest expense										112,784	115,160	121,843
Other expense, net										472	1,524	2,027
Early extinguishment of debt, net	$ 10,524									8,969	0	(11,426)
(Benefit from) provision for income taxes		(56,560)								(18,237)	16,634	22,835
Net income		$ 62,969	$ 44,719	$ 45,173	$ 10,653	$ 13,300	$ 34,658	$ 30,494	$ (10,753)	163,317	67,493	32,779
Net loss attributable to the noncontrolling interest										197	206	166
Net income attributable to Weight Watchers International, Inc.										163,514	67,699	32,945
Depreciation and amortization										56,992	58,749	60,057
Operating Segments
Segment Reporting Information [Line Items]
Operating income										336,857	249,398	235,260
Depreciation and amortization										42,535	45,125	51,228
General corporate expenses
Segment Reporting Information [Line Items]
General corporate expenses										69,552	48,587	67,202
Depreciation and amortization										14,457	13,624	8,829
North America
Segment Reporting Information [Line Items]
Net revenue										910,349	798,827	755,396
North America | Operating Segments
Segment Reporting Information [Line Items]
Operating income										247,587	175,290	140,579
Depreciation and amortization										39,501	41,718	47,128
United Kingdom Segment
Segment Reporting Information [Line Items]
Net revenue										99,989	100,808	124,773
United Kingdom Segment | Operating Segments
Segment Reporting Information [Line Items]
Operating income										19,939	14,199	24,310
Depreciation and amortization										1,205	971	766
Continental Europe
Segment Reporting Information [Line Items]
Net revenue										239,223	210,590	229,147
Continental Europe | Operating Segments
Segment Reporting Information [Line Items]
Operating income										73,689	51,096	62,364
Depreciation and amortization										1,203	1,621	1,861
Other
Segment Reporting Information [Line Items]
Net revenue										57,350	54,677	55,103
Other | Operating Segments
Segment Reporting Information [Line Items]
Operating income										(4,358)	8,813	8,007
Depreciation and amortization										$ 626	$ 815	$ 1,473